A different slant on tyre pressures

Submitted: Monday, Oct 27, 2014 at 21:36
ThreadID: 109948 Views:10608 Replies:33 FollowUps:85
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I ... like most here, have been a great believer in reducing tyre pressures when traversing corrugated/rough dirt roads.

Hence, on our recent trip to the Kimberleys, where we went well off the beaten track up to Kalumburu, Port Warreber (sp?) and into Walcott Inlet from Mount Elizabeth, I reduced pressures to about 36 psi in the rear and 28 psi in the front ... 70 series Cab Chassis with Al rear canopy and perhaps 500kg of stored gear .... (well under GVM), towing Campomatic (maybe 120kg ball weight). OK ... now you have the vehicle details.

Oh.. BTW ... running virtually new 265.75 BFG TA's.

Net result ... the rear pair were chewed to pieces and extraordinarily badly chipped with the fronts only mildly damaged. Dropped in to the local tyre place/tyre supplier for a wheel alignment/rotation and asked about the state of the tyres and did they think they could call in the tyre rep to have a look.

On my return to collect, they showed me the rears (now as deflated spares) which were totally stuffed on the inside with huge bubbles of delamination around the bead near the rims.

In the opinion of the tyre rep failure could be attributed to running at too low pressure. He was adamant they should not go below 46 psi for these loads on these roads.

Got me buggered .... as well as the tyres. As he said ... these fellas can go up to 80 psi, but NEVER below 46 psi under my load conditions .... go figure.
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Reply By: DmaxQld - Monday, Oct 27, 2014 at 21:49

Monday, Oct 27, 2014 at 21:49
On dirt I tun 28 PSI cold all round.

Interesting that the fronts @ 28 were OK. Think that is what you wer saying. So maybe you should have dropped the rears to 28 also.

Would be interested to hear what speed you were doing with the fronts at only 28
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Follow Up By: Freshstart - Tuesday, Oct 28, 2014 at 10:52

Tuesday, Oct 28, 2014 at 10:52
We used 26 rear and 20 front for that road and no chips or cuts. Maybe 36 was a tad (big tad) too high.
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Reply By: Member - Stephen L (Clare SA) - Monday, Oct 27, 2014 at 22:06

Monday, Oct 27, 2014 at 22:06
Hi Rosco

I bet the guy that said that has never seen a corrugated road.

I would love to see the condition or what damage to the vehicle running very high pressures on corrugated tracks. I usually run my Bridgestone LT's at 18 to 20 psi when on such tracks like the Anne Beadell and never had any issues with tyre damage. If I ran even with your rear tyre pressures, the car would be shaken to pieces.

But like all situations, reduced tyre pressure also means lower speeds of travel.

It is either a case of the tyres being faulty, or they were still miles too high.


Just my thoughts.



Cheers



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Follow Up By: Member - Wildmax - Monday, Oct 27, 2014 at 23:25

Monday, Oct 27, 2014 at 23:25
I agree - bet the tyre guy has never seen a corrugated road, or the tyres were dodgy.
We were in the Kimberley this year, including up the Kalumburu Road to Mitchell Falls, running around 24psi in front and 28 in the rear (under a loaded canopy and towing a TVan). That was part of around 10,000 km of dirt, rock, corrugations and the rest - and no problems at all.
The only damage on our whole trip was right at the start with a stake through a side wall coming over the sand dunes on Googs Track, out of Ceduna (running around 16psi at that stage).
I'm using Cooper AT3 light truck tyres, and discussions with Coopers confirm the lower pressure guidance (as does their pamphlet).
But the best advice of all on this topic, in my view, is courtesy of the late and sadly missed Adam Plate, formerly of the Pink Roadhouse at Oodnadatta, who produced a great little hand-drawn set of tyre advice for all conditions.
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Follow Up By: olcoolone - Tuesday, Oct 28, 2014 at 08:03

Tuesday, Oct 28, 2014 at 08:03
Suspension is meant to soak up corrugations and not the tyres or if the corrugations are that bad slow down.

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Follow Up By: Member - Wildmax - Tuesday, Oct 28, 2014 at 10:11

Tuesday, Oct 28, 2014 at 10:11
But suspension is going to be working mighty hard if you're running 45psi !! Still reckon Adam Plate gave the best advice, based on years of his own experience and repairing other people's mistakes.
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Follow Up By: The Landy - Tuesday, Oct 28, 2014 at 10:27

Tuesday, Oct 28, 2014 at 10:27
Wildmax

The advice is generalised and doesn’t take account of vehicle weight or loading. It stands to reason that tyre pressures for a load at 60% of GVM will be different for a load at 90% of GVM.

Putting that aside though, one always needs to drive to the conditions and the vehicles shock absorbers are designed to do just that. Any corrugated road will work suspension harder and driving needs to be adjusted to compensate.

But what you are suggesting is that the tyre does the work of the shock absorber, something it was never designed to do, so your risk is that the “cushioning” you are getting from reduced tyre pressures occurs because your tyre is flexing, and that will produce heat that can (will most likely) lead to tyre failure over time…

Cheers, Baz – The Landy
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Follow Up By: Member - Wildmax - Tuesday, Oct 28, 2014 at 12:15

Tuesday, Oct 28, 2014 at 12:15
Of course I agree driving to the conditions is the first and foremost point of advice. But we've done around 120,000 km over the past four years using the sort of pressures I describe, and tyres have not been an issue at all. Having said that, this is all supported by after market suspension and shocks.
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Follow Up By: olcoolone - Tuesday, Oct 28, 2014 at 20:02

Tuesday, Oct 28, 2014 at 20:02
Buy good suspension and you will find there is a big differance in cheap and exspensive aftermarket suspension. Cheap suspension lacks high and low speed compression adjustment and control.

Too many suspension systems try to be average at everything...... Supose it's hard enough getting people to part with $700 for a set of 4 shocks let alone $3000.

Drive or travel in a well set up suspensined vehicle and it will blow your mind away.

If you don't want to spend big coin on shockers all you have to do is slow down and drive to the suspensions capabilities..... And don't try and make the suspension work better by using the tyres.
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Reply By: Member - Rosco from way back - Monday, Oct 27, 2014 at 22:19

Monday, Oct 27, 2014 at 22:19
Thanks for your thoughts fellas ...
this is what I'm talking about .........

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Follow Up By: Member - Rosco from way back - Monday, Oct 27, 2014 at 22:21

Monday, Oct 27, 2014 at 22:21
PS ... < 20K km
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Reply By: Alan S (WA) - Monday, Oct 27, 2014 at 22:20

Monday, Oct 27, 2014 at 22:20
Rosco

Wife's cousin lives in broome and has, still does go quite remote. His view is unless it's sand you run them hard.

Alan
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Follow Up By: Zippo - Tuesday, Oct 28, 2014 at 15:00

Tuesday, Oct 28, 2014 at 15:00
Not that I have accumulated as many kms on corros as many here, but I always run normal pressures. Anything lower introduces two problems: excessive sidewall flex/heat, and exposure of sidewalls to staking. I have the same philiosophy - if it ain't sand it ain't gonna get lower pressure from me. Lower pressure is for TRACTION and footprint reasons, NOT ride. The suspension is there for a job, and if it isn't up to it you have the wrong vehicle/suspension for the job or you aren't driving to the conditions.
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Follow Up By: mikehzz - Tuesday, Oct 28, 2014 at 19:31

Tuesday, Oct 28, 2014 at 19:31
Sorry but that is ridiculous. They only invented pump up tyres to improve ride quality. Otherwise we would be riding on solid rubber tyres.
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Follow Up By: olcoolone - Tuesday, Oct 28, 2014 at 20:06

Tuesday, Oct 28, 2014 at 20:06
Apart from the cost and weight of running solid rubber tyres you might be onto something there Mike
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Follow Up By: mikehzz - Tuesday, Oct 28, 2014 at 23:00

Tuesday, Oct 28, 2014 at 23:00
You would only need an inch or so around the edge. The rest would be rim, not much risk of denting it as a solid rubber tyre wouldn't flex much. I still remember prefering my new pump up scooter over my old fashioned solid wheel one as a kid though. :-)
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Follow Up By: Ron N - Tuesday, Oct 28, 2014 at 23:56

Tuesday, Oct 28, 2014 at 23:56
Here's your answer to flats and heat buildup - the latest from Michelin.
And if you really wanted to know the answer to your question - they're fitted to a Morris Minor hot rod!
It will be interesting to see how they handle full loads and corrugations at 90-100kmh!

Michelin Tweel
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Follow Up By: Alloy c/t - Wednesday, Oct 29, 2014 at 07:55

Wednesday, Oct 29, 2014 at 07:55
You can now buy solid inserts instead of tubes for Motorbike tyres that are mainly used for mustering , no flats or staking …..
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Follow Up By: MARIC - Thursday, Oct 30, 2014 at 09:47

Thursday, Oct 30, 2014 at 09:47
We have done the Gibb and up to Mitchell Falls and Kalumbaru
Nissan GU Patrol cab chassis running BFG'S 265's, towing van fully loaded 42-46 psi with nitrogen instead of air and no problems. But we had to be carefull of blowouts after the wet season. The road repairs wre done by scooping up rocks from the side of the road and using a padfoot roller. Thus having sharp edged shattered rocks just waiting to stuff up your sidewalls. We would drop tyre pressures on sandy tracks.
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Follow Up By: Ron N - Thursday, Oct 30, 2014 at 11:36

Thursday, Oct 30, 2014 at 11:36
Maric - The largest proportion of all the severe tyre damage I've ever suffered, has been on freshly-maintained roads.
Poor grader operation is what drags rocks, sticks, and roadside rubbish, into the formation.

Properly done, road maintenance with a grader is carried out by making a fairly deep cut right across the width of the formation, producing a windrow at one side.
This takes the ruts out and produces a smooth surface.

You then spread that windrow back across the formation thinly - which separates the rocks, sticks and rubbish out of the windrow and dumps them at the side you started on - while it leaves a thin layer of material to be compacted onto the smooth surface you formed with the initial passes across the formation.

Sometimes, if there's a lot of loose material, you have to do a third series of passes across the formation to get rid of the windrow.
In this case, you sweep the rocks across to the far side of the formation, taking care to keep the spread layer of loose material thin, to ensure the rocks and debris are screened out.

Lazy grader operators merely pull all the rocks and debris from the edges of the formation and pile it into the middle of the formation, and leave the roller to pack it all down, thus trapping all the unwanted rocks and debris into the road surface.
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Follow Up By: Member - Andrew & Jen - Thursday, Oct 30, 2014 at 11:57

Thursday, Oct 30, 2014 at 11:57
Ron N
Agree wholeheartedly.
There should be more with your expertise doing patrol and maintenance grading.
There is also really no excuse for the number of base/sub-base failures in cuts due to a failure to properly maintain good table drains.
Both of the above is, IMHO, also due to poor supervision / training.
Cheers
Andrew
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Follow Up By: MARIC - Saturday, Nov 01, 2014 at 11:14

Saturday, Nov 01, 2014 at 11:14
I agree with Ron,
However The Gibb does not have much gravel, as I stated 'rocks' crushed, my family worked with Main Roads WA prior to retirement
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Reply By: Member - Nutta - Monday, Oct 27, 2014 at 22:50

Monday, Oct 27, 2014 at 22:50
Personally i think the bfg's are way overrated, the best tyres I've owned would have to be bridgestone dueller d697's, bullet proof imo!
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Follow Up By: MARIC - Thursday, Oct 30, 2014 at 09:54

Thursday, Oct 30, 2014 at 09:54
Perhaps but all our driving is off road 3 sets and over 270,000ks total so we are happy with them
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Reply By: Ron N - Monday, Oct 27, 2014 at 23:30

Monday, Oct 27, 2014 at 23:30
Rosco - Those tyres show a classic case of sidewall overheating and carcass failure, due to running too low pressures.
Remember, that as you reduce tyre pressures, the more the sidewall flexes.
Increased sidewall flexing means rapid heat buildup - rapid heat buildup means destroyed tyre carcasses.

I have never reduced tyre pressures for corrugated roads. If you are going to do so, you need to reduce road speed by a substantial amount - and I mean substantial.

Imagine your tyre sidewall is a piece of heavy wire between your hands.
You can move your hands back and forth, flexing that wire, and if you don't do it too fast, you can keep doing that for an hour - the wire will not heat up substantially, and it will not fracture.

Now, start moving your hands back and forth rapidly and that piece of wire heats up to the extent it will burn you, if you put your hands on it - and it will fracture and break in two within 30-45 seconds.

A tyre sidewall performs exactly the same as that piece of wire. The sidewall might be rubber and rayon or steel cords - but it produces heat and failure with excessive flexing, exactly as that strand of heavy wire does.

Years ago, we used to run an old WW2 low-loader that was fitted with 8.25x15 tyres for low deck height.
Truck radials were virtually unheard of in those days (apart from Michelins), and those crossply 8.25x15's would run as hot as hell with regular speeds of 70-80kmh and around the recommended 70-75psi, when loaded. On hot days, those tyres would pop like party balloons.

We had discussions with tyre reps, and they recommended we run the tyres at a minimum of 100psi and preferably 110-120psi. We did so, and those crossplys stopped blowing like party balloons and we even managed to run some through to full tread wear.
The pressure increase was all about stopping the sidewall heat buildup by pumping the tyre up and reducing the sidewall flexing. It worked.
The old WW2 low-loader was designed to be used behind the likes of WW2 Diamond T's and Federals - that were flat out at 50kmh.
At that speed, the 8.25x15 crossplies performed quite satisfactorily at the WW2 recommendation of 70-75psi.

It was only with later model faster trucks, that the tyres started giving trouble. At the low WW2 speeds, the heat buildup from the tyre flexing wasn't really measureable. At higher speeds, it became a major problem.

Incidentally, BFG's are not my favorite tyre, either - I have never had satisfactory performance from any BFG's I've ever bought, or that were fitted to new vehicles I purchased.

Cheers, Ron.
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Follow Up By: Member - Rosco from way back - Monday, Oct 27, 2014 at 23:44

Monday, Oct 27, 2014 at 23:44
I'm afraid I have to agree with you Ron on the failure mode. This has been my first foray into BFG's, so I'll give them the benefit of the doubt and replace the two buggered ones with same. Then see how they go. On the one hand I'm disappointed with their performance to date, but then again we did not get a single flat, whereas last year on the GRR running OEM Dunlops we had no end of grief and destroyed a number at various pressures.

I was quite impressed with Wrangler MTR's on a previous vehicle or even the OEM General Grabbers. May have to rethink the whole thing. Only went with BFG'a after hearing lots of positives.

I certainly agree it looks mighty like low pressure failure.
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Follow Up By: Ron N - Tuesday, Oct 28, 2014 at 00:45

Tuesday, Oct 28, 2014 at 00:45
Good God, Dunlops! They aren't nicknamed "Banglops" for nothing.
I bought a Mack cabover prime mover in 1975 that was fitted with a mixture of Dunlop and Michelin tyres. Without fail, every single Dunlop fitted to that truck blew out before I could get full tread wear out of it.

In comparison, all the Michelins went to full tread depth and were then recapped and recapped again.
Not a single Michelin ever blew out in the 18 years that I owned the truck.

I once bought 4 new Dunlops for one of my Holden utes and all 4 Dunlops suffered carcase separation, to the extent they went so badly out of round, it was nearly impossible to hold the ute on the road, such was the imbalance.

A mate bought a new Mini Cooper S in the late 1960's and it was fitted with Dunlop SP40's all round from the factory. The SP40's were reputed to be the ducks gonads.
The Mini was 3 weeks old when Arthur decided to "give it a wrap" and wound it up to 100mph (160kmh) on a nice straight stretch of country highway - with 3 mates on board.

Two SP40's blew out at that speed in quick succession, and Arthur lost control, the Mini left the road - somersaulted 3 times through a concrete culvert entrance, split in half at the bottom of the windscreen posts (a bad habit of Minis), and ended up back on its wheels on the far side of the culvert.

The roof had peeled right back, and all four blokes in the Mini just unfastened their seatbelts and stood up, there was nothing above them!
To say that Arthur promptly developed a life-long hatred of Dunlops is an understatement.

In 1997, I purchased a 32' (10M) tri-axle car transporter trailer that had previously been a 40' (18M) Viscount caravan transport chassis (this was a separate trailer frame, where the trailer could be taken away from the caravan).
The Viscount trailer frame had been converted into a tri-axle car transporter and fitted with 6 new Dunlop 195Rx14C tyres.
I didn't use the trailer as much as I had envisaged (probably less than 5000kms) and I sold it in year 2000.

The bloke who bought the trailer, told me a year later, that every single Dunlop on that trailer had blown out - and cost him a heap of money in replacement tyres - when he thought when he bought the trailer, that he would have no tyre costs, for a couple of years at least!

Cheers, Ron.
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Follow Up By: The Landy - Tuesday, Oct 28, 2014 at 08:16

Tuesday, Oct 28, 2014 at 08:16
I’m in agreement here, based on my own experience.

“The Landy” comes in at around 3,500kg (3,900 GVM) in touring mode with the TVAN, and with the canopy the rear axle weight, whilst within specifications, is high.

The reality is that with this sort of weight one needs to be very cautious dropping tyre pressures too low. As Ron has highlighted, low tyre pressures require an adjustment in speed, and I will add considerable reduction.

Whilst there may benefits to reducing tyre pressures in certain situations, it should only be done after considering the ambient temperatures, weight of the vehicle and load it is carrying, and speed at which you are or will travel at.

But importantly, a reduction in tyre pressure is usually done to ensure full traction for the vehicle. If you are getting traction then you need to ask why the need to drop pressures.

In my opinion there are far greater risks from sidewall failure due to tyre pressures being too low, versus the increased risk of vehicle damage or punctures from having them too high. And the problem with sidewall failures is that the damage, having already been done, may not manifest until you have a high-speed blow-out on the black tar heading home from a trip.

I regularly see guidance on what tyre pressures should be run vs. the road surface being driven on, with absolute pressures being expressed. It isn’t logical to the extent it does not take account of the vehicle weight, road conditions and ambient temperatures.

Traction is what you are endeavouring to achieve so run the highest pressure that achieves it…

Adding, on corrugated roads, drop your speed, substantially if needed!

Cheers, Baz – The Landy
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Follow Up By: Bazooka - Wednesday, Oct 29, 2014 at 21:33

Wednesday, Oct 29, 2014 at 21:33
<20km? Sounds more like a classic case of poor manufacture (possibly assisted by low pressure/high temp) if you ask me. There have been a few rumblings around about recent BFGs iirc. Don't know if it's any more than background noise but it's something which was "never" heard 10 years ago. They were virtually the grail. I'd be more than disappointed if a tyre of that size couldn't be run at that pressure/load for a far longer period without causing damage.
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Follow Up By: Echucan Bob - Friday, Nov 07, 2014 at 18:58

Friday, Nov 07, 2014 at 18:58
The things that destroy tyres are speed and load. You should deflate your tyres for corrugations but if you are overloaded you will get too much side wall bagging. Then, if you travel too fast the constant flexing caused by the side wall bagging creates heat that builds up and leads to delamination of the tyre.

We ask too much of our tyres by loading our vehicles excessively. Ideally, touring vehicles would have double wheels at the back. Until that happens, we should leave as much crap at home as possible, and slow down.

To those who leave their tyres at 45 psi and more, I hope you carry spare shocks.
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Reply By: Nomadic Navara - Tuesday, Oct 28, 2014 at 00:12

Tuesday, Oct 28, 2014 at 00:12
Did you drop your speed as well as the pressure? 40 - 50 km/h max with reduced pressures.
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Reply By: Sigmund - Tuesday, Oct 28, 2014 at 06:06

Tuesday, Oct 28, 2014 at 06:06
I follow Adam Plate's advice and reduce pressure by 30% on corro and gibber. D694s and D697s driven at up to 80 kmh - never had a problem.

This is the first post I've seen with evidence of one after following common practice among 4WDs. I suspect the tyres rather than the pressure, esp as it's two out of four.
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Follow Up By: OBJ - Tuesday, Oct 28, 2014 at 08:24

Tuesday, Oct 28, 2014 at 08:24
X2 for Adam Plates tyre pressure advice. I take his print-out everywhere.
OBJ
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Follow Up By: Alloy c/t - Tuesday, Oct 28, 2014 at 09:14

Tuesday, Oct 28, 2014 at 09:14
One thing that people forget is that the "pink roadhouse" has / had a vested interest in selling tires ,, vehicle manufactures spend big $$$$ in conjuction with tire manufacturers to get the correct tire pressure for the vehicle suspension to be able to perform as designed...
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Follow Up By: olcoolone - Tuesday, Oct 28, 2014 at 19:52

Tuesday, Oct 28, 2014 at 19:52
Tyre technology has come in leaps and bounds over the last 5 years and many ideas came about from people who used old technology tyres.
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Follow Up By: Sigmund - Thursday, Oct 30, 2014 at 10:34

Thursday, Oct 30, 2014 at 10:34
Vested interest in selling tyres? You're saying that they'll send people out expecting them to trash tyres so they'll come back and buy some.

That's a pretty libelous statement. What's your evidence?
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Follow Up By: Alloy c/t - Friday, Oct 31, 2014 at 09:44

Friday, Oct 31, 2014 at 09:44
Simund .. libellous statement ? Pray tell how so , sells tires as part of his business interests and gives printed ambiguous advice that is contrary to manufacturers advice …. libellous Yeah right , the only person who has stated ' send people out to trash their tires so they come back to buy more ' is yourself !
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Follow Up By: Sigmund - Friday, Oct 31, 2014 at 10:16

Friday, Oct 31, 2014 at 10:16
Then what do you mean by 'vested interest'?
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Follow Up By: Alloy c/t - Friday, Oct 31, 2014 at 10:28

Friday, Oct 31, 2014 at 10:28
Sigmund , look it up in a dictionary if you don't know the correct meaning of the word , no different in saying a Toyota dealer / salesman has a 'vested interest' in selling you a Toyota , Libellous Statement ???
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Follow Up By: Sigmund - Friday, Oct 31, 2014 at 10:47

Friday, Oct 31, 2014 at 10:47
You linked an interest in making money from selling tyres with giving out advice on tyre pressures that may be contrary to manufacturer advice. Own the implication or disown it.
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Follow Up By: Alloy c/t - Friday, Oct 31, 2014 at 11:13

Friday, Oct 31, 2014 at 11:13
Sigmund , make of the term 'vested interest " whatever you want , a man that sells whatever it maybe ,being tires or cars or a hamburger has by definition a ' vested interest ' in the transaction , no demeaning implication was or is inferred ..
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Follow Up By: Ron N - Friday, Oct 31, 2014 at 14:40

Friday, Oct 31, 2014 at 14:40
I've got a mate who owns a country tyre shop - and we always crack jokes with him about him going out and spreading a few handfuls of tacks around the streets, when business is slow!
He takes it all in good humour, he's a pretty good wisecracker himself.

However, to suggest that a tyre business is handing out suspect information about tyre pressures and loads to garner increased sales is probably stretching the truth greatly.
There's no way a tyre shop could ensure that a client handed dodgy tyre advice would generate increased tyre sales for that particular shop.

In nearly every case, if these reputed attempts at increasing sales by handing out dodgy advice was true - then the client would be 500kms away and into other tyre shop territory, before the damage was incurred. Thus there would be absolutely no benefit to the tyre shop handing out the dodgy advice.

The major problem with tyre shops is unscrupulous operators claiming that a tyre is damaged beyond repair when it's not.

Years ago, in the age of tubed tyres, a farmer client had a son and DIL who owned a tyre shop in a far Northern W.A. town. The iron ore rush was already on, and speed was crucial and costs were unimportant to many clients.

As a result, any flat tyres that were presented with just a nail/road debris hole in the tyre and tube, were never repaired with a patch. The client was always told the tube was unrepairable and a new tube fitted. This not only speeded up repairs enormously, it also greatly increased the tyre shops turnover.

The fact that many excellent tubes that only needed a patch, were totally discarded, was irrelevant in the rush for speed and increased turnover.

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Reply By: Sand Man (SA) - Tuesday, Oct 28, 2014 at 07:35

Tuesday, Oct 28, 2014 at 07:35
Hi Rosco,

We drove the Kalumburu Track towing a Campomatic up as far as Drysdale River and back and also the Cape Leveque Road and Middle Lagoon Tracks which were pretty bad in parts. The ball weight on my loaded rig is closer to 180kg.
I ran the tyre pressures at 32 rear, 28 front in the Colorado and experienced no problem at all. I run Bridgestone 697 LT AT's and at no time did I feel heat in the sidewalls. The camper tyres were also defated to 32psi from my normal highway pressure of 38psi all around.

Deflated the tyres at El Questro and left them that way all the way down the Gibb, out to Drysdale R.S. to Broome, then out to Middle Lagoon and back along the Cape Leveque road which is unsealed up to the Middle Lagoon turnoff at least.

I was nearly going to ask you if the tyres were Coopers:-) until I saw the picture of the BFG's.

Really pleased with the performance of the Bridgestone light truck rated 697's which have stronger side walls than the older 693's and 694's and I will continue to use them both on the vehicle and camper.

I cannot see how tyres that do not allow flex in the sidewalls can be considered both easier to drive, perform better on unsealed roads as they "mould" to the changing road surface and give a more comfortable ride can be considered as practical for off road use.
The rigid unflexing sidewalls must cause the tyres to continually bang down on the road surface giving a horrible ride and further damage the track surface as well.

Bill


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Reply By: olcoolone - Tuesday, Oct 28, 2014 at 07:58

Tuesday, Oct 28, 2014 at 07:58
A few years ago we went away from running low tyre pressures, the only time we drop to a lower pressure is in sand..... but on most other surfaces we stay at highway pressures.

So far no funny tyre wear, chipping or damage.

Have had a few friends start doing the same with no ill effects.

And as for damaging the environment....... show the data that says higher pressures cause more damage on harder ground (not talking about sand).
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Reply By: Member - Oldbaz. NSW. - Tuesday, Oct 28, 2014 at 09:00

Tuesday, Oct 28, 2014 at 09:00
I have used the same tyres towing a C/t or caravan on all the main corro roads..
Plenty, GCR, Tanami, GRR etc & never reduced pressure below 38psi cold. No tyre
damage, no vehicle damage. No need to travel at reduced speed either. Heat kills tyres & the quickest way to stuff them is reduce pressure & not speed. In my last life
as a contract boom sprayer, the tyre damage stopped when I got to 60 psi, & no, I
don't subscribe to that balloon & pin theory. Every tyre troubled poor sod I encountered on outback roads was running lowered pressure.
I don't expect to change the "air up/down" brigade, but I know what works for me.
cheers.....oldbaz.
AnswerID: 540955

Follow Up By: Alloy c/t - Tuesday, Oct 28, 2014 at 09:23

Tuesday, Oct 28, 2014 at 09:23
Yep , recon that the only time to drop pressure from the vehicle manufacturers tire placard is on sand to increase the 'footprint' , excessive heat buildup kills tires , the 4psi rule 'RULES'..
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FollowupID: 826884

Reply By: Member - Norm & Lisa - Tuesday, Oct 28, 2014 at 09:35

Tuesday, Oct 28, 2014 at 09:35
Howdy - Just back from 18k of touring including Gibb, Kalumburu, Cape Leveque, Tanami, Oodnadatta and Birdsville... and probably one of the worst bits from Birdsville to Windorah. Total casualties were 3 tyres - Goodyear Wranglers Silent Armours 265/70/16 on V8 Landcruiser Ute with Alum Canopy and 200kg ball weight. The ute has an upgraded GVM to 3760 and we were at around 3500kg. Dropped the pressures to around 26 in the front and 36 in the back and I don't drive fast. A mate running Bridgestones dropped tyre pressures even further and went through a similar number of tyres. Again with his Hilux loaded up with a sleeper on the back. My tyres all went in the bead which started to split and then slowly leak air. When noticed I took them off to find the leak and when I saw the split beads they didn't go back on.
I think I am joining those who believe in keeping the tyre pressure up, the tyre temps down and the speed down. I have the drawing from Adam Plate and if I remember correctly, he states on the drawing that the pressures are for high speed dirt driving conditions so my thinking is to keep the pressures up and the speed down and hopefully all will be good for the next trip. I will also be looking at different profile tyres to 265/75 or even 285/75 but the priority when buying will be load rating.
Everyday is a holiday
Norm & Lisa

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AnswerID: 540957

Follow Up By: The Landy - Tuesday, Oct 28, 2014 at 10:21

Tuesday, Oct 28, 2014 at 10:21
I have a Dual Cab 79 Series, which has a GVM of 3,900kg and loaded when touring to around 3,500kg with the TVAN in tow.

With that weight I don't deflate to any great extent, and run at around 40psi.

The problem with the "generalised" tyre pressure advice is just that, it is generalised and doesn't take account of vehicle loading or weight.

What might be appropriate at 60% of GVM may not be at 80 or 90 % of GVM, and given many vehicles are in touring mode, weights are generally higher than lower. The risk of sidewall damage due to heat flexing, and which may not necessarily be visible increases with lower pressures...

And given this is a topic that could consume the forum forever, do as Yogi philosophy suggests...accept as truth that you can prove for yourself...

Cheers, Baz - The Landy


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Reply By: Member - Nolo (Brisbane) - Tuesday, Oct 28, 2014 at 10:06

Tuesday, Oct 28, 2014 at 10:06
I also have a 79 Series with a "heavy" canopy on the back. My experience on fast dirt has been to run the rears up to 10 psi higher than the front due to the weight on the rear. I experienced the same on a recent 17,000 km trip to the Kimberley in a 200 Series, also heavily loaded in the back. This is borne out by monitoring the pressure increase over all tyres through a Tyre Pressure Monitor System, a must have accessory in my opinion.

I don't believe the brand of tyre has as much to do with failure as inappropriate pressures run (again on fast dirt). Get yourself a good TPMS unit - you will be surprised at the variances from cold to hot.
AnswerID: 540958

Reply By: Ron N - Tuesday, Oct 28, 2014 at 10:14

Tuesday, Oct 28, 2014 at 10:14
Re corrugations in gravel roads, here's a webpage with a proper scientific experiment as to how and why corrugations ("washboard" to the rest of the world) are formed.

What causes "washboard" in roads?

Note how the boffins state .. "The fact that our simplified systems produce washboard ripples is important, since it shows that neither tyres nor suspensions are necessary to obtain washboard roads; although of course, adding a spring, a dashpot, a tyre or an engine, would affect the size of the bumps.
In other words, it is not because of the suspension of cars that washboard roads exist. The ripple wavelength is NOT simply the speed of the wheel times the bounce frequency of the suspension, which seems to be a common belief."

Note also how they find that the speed factor is crucial. However, this is what they find! ...

"The speed of the wheel appears to be crucial. Indeed, there exists a critical velocity below which the road always remains flat, and above which, washboard bumps appear. Typically, for a car, this critical velocity is around 5 mph or 8 km/h." (!)

The bottom line is that you will get corrugations on loose gravel regardless of tyre pressures, speed, or vehicle weight.
It's the grain content of the road surface, and looseness of the material that governs whether corrugations appear.

You will notice how many sections of gravel roads do NOT corrugate. This is because the clay content of those road sections is higher, and the road surface sets hard because of good inbuilt bonding chemicals, and clay, in the road base.
However, road base with higher clay content tends to become slippery when wet, therefore sandy gravels are chosen for road base, for gravel roads.

Finding and producing good road base gravel, is a black art.
Many shire operators and foremen have inadequate skills in these areas, and they always tend to select gravels that are too high in sand content, and which rut and corrugate swiftly.

Another contributing factor is wear in motor grader blade linkages. As someone who is a qualified grader driver, who has owned numerous graders, and who has done thousands of hours of grading - I can assure you that grading at speed with worn blade linkages sets up initial corrugations in the formation. Car wheels then just accelerate the corrugations.

I have even come across sections of bitumen where a grader with worn blade linkages was used to do the final grade work before sealing - and they managed to get corrugations into the final finish before bitumenising - and those corrugations were then sealed into the bitumen!
AnswerID: 540959

Reply By: Gronk - Tuesday, Oct 28, 2014 at 10:22

Tuesday, Oct 28, 2014 at 10:22
What no one has mentioned is when they dropped pressures, how fast did they travel ??

Dropped pressures and a steady 70 k/ph would be fine, but get to 80 or 90 k/ph and a hot day as well, then heat is going to kill them.

I had a rear tyre go on me along Cordillo Downs road a few yrs back ....dropped pressures to 28 psi, towing a camper as well, and speeds gradually crept back up to around 80 or 90 k/ph ( the road got that good we could have gone faster )

Other rear tyre ( the good one ) was very hot to touch ( it failed 2 months later just driving along- a blowout ), so nowadays I'm very wary of when I reduce pressures. Went from Yunta to Arkaroola 2 yrs ago and reduced pressures to 30 psi, but set the cruise control to 70 k/ph and all was good, but if I was travelling like the rest of the people in a hurry to get there, I wouldn't have bothered ..
AnswerID: 540960

Reply By: Grizzle - Tuesday, Oct 28, 2014 at 11:18

Tuesday, Oct 28, 2014 at 11:18
I keep my pressures low when offroad BFG A/T Nissan Patrol loaded up. 24-28 rear, 20-24 Front.

But as a curly one to throw in I talked to a guy years ago and he MEASURED the footprint of each tyre on the road. I can't remember the length but he let the tyre down until he had a set amount of tread on the road.

Would certainly cater for differing loads etc.

One to ponder!!

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AnswerID: 540967

Follow Up By: Member - Munji - Tuesday, Oct 28, 2014 at 11:51

Tuesday, Oct 28, 2014 at 11:51
I have done the GRR and Kalumburu Road twice in last three years. Once with a Nissan Patrol and once with a Toyota Prado (Towing a 2000 kg camper).
Both times fitted with AT tyres, pressures down to 36 psi front and rear. Tough Dog adjustable foam cell shockies (backed off to low setting) and kept my ave speed between 50-70 km/h.
Not one single issue with the tyres on both vehicle and camper.
First set were BFG and second set were Bridgestone Dueller 697.
One chap was about to go home at Drysdale, he asked me what was my set up so he dropped his tyre pressures from 45 back to 36 and when I spoke with him at Mitchell Plateau he said the ride was better and the tyres were not running any hotter and kept his speed between 50-70 km/h.
Both trips my GVM was about the same, people need to experiment a little when doing these trips so they can get a good balance with the own set up.
I agree, that too much deflation will cause sidewall damage if combined with too much load and too much high speed.
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Follow Up By: The Bantam - Wednesday, Oct 29, 2014 at 11:35

Wednesday, Oct 29, 2014 at 11:35
There is a thing that is easer and more accurate than measuring footprint length.....AND it is engineered and documented and quite accurate.

Measuring hub centre height.

once you have established an appropriate pressure for the load carried and for the situation in hand.

Measure the hub centre height on a good flat surface........as the load changes maintain the same hub centre height and the pressure for load relationship that was previously established will be maintained...as willbe the length ofvthe footprint.

cheers

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FollowupID: 826979

Reply By: Grizzle - Tuesday, Oct 28, 2014 at 11:30

Tuesday, Oct 28, 2014 at 11:30
Oh, and forgot to mention I also think Adam Plate's sheet is excellent!!

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AnswerID: 540968

Follow Up By: Grizzle - Tuesday, Oct 28, 2014 at 12:30

Tuesday, Oct 28, 2014 at 12:30

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Follow Up By: Grizzle - Tuesday, Oct 28, 2014 at 13:09

Tuesday, Oct 28, 2014 at 13:09
Try Again

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Follow Up By: Member Kerry W (WA) - Thursday, Oct 30, 2014 at 01:46

Thursday, Oct 30, 2014 at 01:46
Agree! Problems will arise with lower profile tyres at low pressure.
Kerry W (Qld)
Security is mostly a superstition. It doesnt exist in nature. Life is either a daring adventure or nothing.
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Reply By: Ron N - Tuesday, Oct 28, 2014 at 13:11

Tuesday, Oct 28, 2014 at 13:11
Adam Plates diagrams and suggestions are interesting - but they go against nearly all tyre manufacturers recommendations.
Does anyone remember that the multitude of early Ford Explorer crashes were sheeted home to engineers reducing tyre pressures to get a smoother ride? - which caused an increase in tyre failures? (usually associated with high speed vehicle useage).
Ford later revised tyre pressures upwards and the incidence of Ford Explorer crashes caused by tyre blowouts reduced enormously.

Adam has one suggestion there that it's O.K. to reduce 'Big 4WD 15" tubeless loaded' pressures to 20psi front and 26psi rear - and then adds, "These suggested tyre pressures are for high load, HIGH SPEED cruising, on low grip dirt surfaces and rock or sand".

Now, I'm not sure what Adam is referring to, by "high speed" - but to most people, "high speed" relates to highway cruising speeds of around 100kmh.

I would respectfully suggest that anyone who reduces their 15" 4WD tyre pressures to 20 and 26psi respectively - and who then travels at 100kmh with a full load - is asking for tyre trouble, in the exact manner that Rosco has experienced.

I wouldn't have a problem with someone reducing their tyre pressures to those levels to try and improve their ride - but speed of travel would then have to be at a substantially reduced rate - say around 70kmh, or 80kmh at most.

A simple test to check if your tyre sidewalls are under threat from excessive heat buildup, is to place your hand on the sidewall after travelling some 25-30kms with reduced tyre pressures.

If the tyre sidewalls feel hot enough to the touch to be uncomfortable holding your hand there for a constant 20-30 seconds, then they either need more pressure in them, or you need to reduce your road travel speed by a substantial amount.

A tyre running at a satisfactory temperature should only feel warm to the touch, not hot enough to be uncomfortable on bare skin.

The lifespan of your tyres is directly related to its operating temperatures during its life cycle. A tyre regularly operated at high temperatures will suffer from a shorter lifespan.

This is because not only does high temperatures in tyre rubber affecting the bonding of the rubber to the carcass material - but high temperatures also result in breakdown of the rubber composition.
In tyre manufacturer parlance, this is known as "oxidative breakdown".

Another little understood factor in tyre pressures, is that if you reduce tyre pressures substantially to improve the ride, you are effectively making the tread conform more to the road surface.

Thus, if you have a corrugated road surface, and you're running low pressures, your tyre tread is also flexing at a considerably higher rate, as compared to running higher pressures - thus leading to additional heat buildup - adding to the increased heat buildup from the sidewalls.
AnswerID: 540973

Follow Up By: Grizzle - Tuesday, Oct 28, 2014 at 15:57

Tuesday, Oct 28, 2014 at 15:57
You do make some valid points there and the underlying consideration for all of our comments should be speed!!

If you take speed out of the equation almost all problems disappear.

Excessive heat, chipping etc would in most cases not happen.

Also (which may not be relevant in this case) a lot of people think because the road is relatively flat they can use 2WD. I was told years ago that as soon as you leave bitumen you should put your vehicle into 4WD if it is not full time 4WD.

I do the above and never go over 80kph regardless of the condition of the road if it is dirt or gravel.

Fingers crossed have never had a puncture due to heat or high speed, only when I have hit something!!!

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Follow Up By: gbc - Tuesday, Oct 28, 2014 at 17:20

Tuesday, Oct 28, 2014 at 17:20
If you read all of it it says that a 15 running more than that is unreliable. What he is alluding to is that p rated tyres require much less air to carry a specific load than an lt. He makes the assumption that all 15's are p rated and all 16's are basically lt's but I agree with his basic premise. With that in mind I can't fault a single one of his diagrams
Anyone saying that he was in the business of selling rubber (couple of posts up) really needs to either do some study or reasses their reasons for being on a forum such as this - I find it downright offensive.
I also agree with you that Adam's idea of high speed and a city slickers assumption of 100kph would be a fair way apart.
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FollowupID: 826919

Follow Up By: Alloy c/t - Wednesday, Oct 29, 2014 at 10:26

Wednesday, Oct 29, 2014 at 10:26
gbc ,perhaps you need to do some research on the ' $ value ' of tires sold by the pink roadhouse on an average year or that the Mungerannie hotel where $30,000 worth of tyres are sold in the tourist season in the lead up to the Birdsville races …..
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FollowupID: 826972

Follow Up By: gbc - Wednesday, Oct 29, 2014 at 18:45

Wednesday, Oct 29, 2014 at 18:45
So geese heading out from town on the wrong pressures stuff their tyres half way? I have no idea how you are going to link all of this into a conspiracy but I'm happy to watch you try. For the time being, my opinion stands.
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FollowupID: 827020

Follow Up By: AlbyNSW - Wednesday, Oct 29, 2014 at 19:28

Wednesday, Oct 29, 2014 at 19:28
Alloy CT I think it is pretty poor form to slander these outback roadhouses in the manor you have without any evidence to support it other than drawing your own conclusions
I have little experience with the Pink Roadhouse but have had many dealings with Phil at Mungaranie
When we stay there we give the bar and the restaurant a good nudge and have had tyre repairs done there as well and we have always been charged less than he is entitled to when settling our account before departure, even repaired a tyre at no charge. This behaviour does not coincide with a money hungry conspirator giving out out false information to the public to gain business
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FollowupID: 827025

Reply By: 671 - Tuesday, Oct 28, 2014 at 13:28

Tuesday, Oct 28, 2014 at 13:28
Rosco

Do yourself a favor and contact BFG through their customer information service. It is in their interests to set you off on the right track in order to get the best out of their products. That is what it is there for.

I have done that for years whenever I buy a different brand or type of tyre. I rang the manufacturer of my current set of standard size commercial tyres (now 7 years old) and had a 20 minute talk with one of their tyre engineers. He even talked about Outback tyre testing programs that he had been involved in where the object was to deliberately destroy tyres.

Two things that came out of our discussion was do not reduce the pressures no matter what the road surface is like and the weight each 1 psi increase would support. The factory recommended pressures are so low anyway that I would have to be out of my mind to want go any lower.

To my surprise those constant pressures have worked perfectly on every surface from the VHC to the Gunbarrel Hwy to freeways in mid summer without the slightest sign of a problem. Of course the same may not apply to all the tyres in their range so if I bought something else I would be back on the phone again.

Give it a try. Your tyres were not designed to fail when used properly so start with the people who made them
AnswerID: 540974

Reply By: Member - KBAD - Tuesday, Oct 28, 2014 at 15:04

Tuesday, Oct 28, 2014 at 15:04
Ran a OKA bus across the Gibb for a couple of years always fully loaded truth is overloaded, had fat radial Michelin tyres on it as it came out of the desert run near Alice, ran 70psi all round had one puncture in two and half years and that was from a bolt. My family ran 9 ton trucks and a single trailer semi on the Gunnawarra Road in Queensland carrying railway sleepers back when it was described the roughest road in Australia (by around Australia rally) always ran 90psi in the tyres. We had blow outs but only on the really hot days but not to many of them then either. It is always a combination of factors, and tyre design and quality will of course have a large bearing.
AnswerID: 540982

Reply By: Member - Rosco from way back - Tuesday, Oct 28, 2014 at 15:19

Tuesday, Oct 28, 2014 at 15:19
To all those posing the question of our speed at reduced pressure: I very much doubt we would have exceeded 80 for any appreciable distance with a good deal of the time as low as 10 through the more tricky sections.
AnswerID: 540983

Follow Up By: gbc - Tuesday, Oct 28, 2014 at 16:47

Tuesday, Oct 28, 2014 at 16:47
My 2c says that those tyres in the picture suffered from 2 unrelated problems. Chipping tyres is from being overinflated - no question. It will happen in 15 minutes on the right surface.
As alluded to, the sidewall blowouts are from overheating.
What is the answer? Haha good bloody question. Personally I'd be looking at bigger tyres again - simple physics of air volume required to carry a certain weight. I.e. Bigger tyres need less air pressure to carry the same weight. That kills two birds straight away, but creates issues around gearing, fuel, legality etc.
It may well be that the correct pressure for the particular surface you were driving on was less than you had, and the correct speed for that pressure was even less than you were doing considering the loaded state of the vehicle.
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FollowupID: 826913

Follow Up By: Ron N - Tuesday, Oct 28, 2014 at 17:20

Tuesday, Oct 28, 2014 at 17:20
Rosco - There's another factor in the equation here, too - the accuracy of your tyre gauge.
With the proliferation of Chinese gauges and their "near enough-good enough, to the nearest 20psi" accuracy, one has to be very careful to invest in a good quality gauge that will cost plenty, but which will give you accurate readings.
At 26 psi, you don't want a 10 or 15% inaccuracy in your gauge.

I have a Michelin 270 deg rotary dial gauge that I bought probably more than 35 yrs ago, and it still provides excellent accuracy. It often indicates that the Chinese gauges are up to 15% out.
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FollowupID: 826918

Follow Up By: Member - Rosco from way back - Tuesday, Oct 28, 2014 at 18:36

Tuesday, Oct 28, 2014 at 18:36
Hopefully gauge accuracy shouldn't be an issue. I had it calibrated recently and it was reading 6 psi high, so I take that into consideration when checking pressures.
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FollowupID: 826922

Follow Up By: DmaxQld - Tuesday, Oct 28, 2014 at 21:52

Tuesday, Oct 28, 2014 at 21:52
Ron N, who do you know you old guage is still accurate?

Rosco, where did you get your guage calibrated?

Thanks
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FollowupID: 826939

Follow Up By: Member - Rosco from way back - Wednesday, Oct 29, 2014 at 00:07

Wednesday, Oct 29, 2014 at 00:07
Calibrated at said local tyre shop against hopefully accurately known pressure.
On a side issue, a bro of mine spent some time working in a tyre shop mob up north some years ago and they were quite anal about calibration of pressure gauges, which I would hope applies across the board.
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FollowupID: 826949

Follow Up By: Ron N - Wednesday, Oct 29, 2014 at 01:01

Wednesday, Oct 29, 2014 at 01:01
DmaxQld - It's still accurate because I treat it like the precision instrument it is, I don't abuse it, and it always resides in its set position in my toolbox - and because I check it against a top quality, liquid-damped test gauge about every five to eight years.

In addition, the rotary dial bourdon tube tyre pressure gauges are far superior to the PCL sliding indicator style of tyre pressure gauge/inflator that many service stations use. The sliding indicator style are notorious for inaccuracy.
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FollowupID: 826951

Follow Up By: The Bantam - Wednesday, Oct 29, 2014 at 10:15

Wednesday, Oct 29, 2014 at 10:15
Tyre shop being anal about calibrating......oh don't make me laugh.

I was selling high quality tyre guages a while back.....I enquired about getting one calibrated just out of interest to see exactly how accurate they where.

Trust me...no tyre shop is going to pay the freight let alone the cost of getting a tyre guage "calibrated" in a properly certified lab....

If they are not going to an instrument lab.....what standard are they using for calibration.....serilulsy I'd like to know......it the price was reasonable I'd buy one.

All they will be doing is comparing with another non calibrated guage.

If they claim anything else.....ask to see the certificates...and there should be calibration tags on the guages..and they should be in date.

Every tyre shop I have every been to over inflates tyres and not by a little either.


all that said...and knowing that there are some realy crappy tyre guages out there.......there are a few good tyre guages that are pretty accurate.....like within 1 or 2 psi..and iff looked after they stay that way for a long time.

cheers

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FollowupID: 826970

Follow Up By: The Bantam - Wednesday, Oct 29, 2014 at 10:18

Wednesday, Oct 29, 2014 at 10:18
OH...if your tyre guage is reading 6psi high...seriuolsy 6psi...

Either you need to toss it or the tyre shop guage is under reading......the more likly thing.

cheers
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FollowupID: 826971

Follow Up By: Member Kerry W (WA) - Wednesday, Oct 29, 2014 at 12:07

Wednesday, Oct 29, 2014 at 12:07
I agree with gbc sometimes failure is 2 unrelated issues. All the technical specs and measurements go out the window in the bush and when extra stress is put on the tyre (heat, extra weight, age of the tyre, compound in the tyre, surfaces driven over, pressure, speed,previous damage etc etc).

The only way to avoid this is to go over spec if you can ie larger stronger tyres. Some of us get it right some don't. It is a learning curve and as I mentioned it comes down to nouse and experience and a firm grasp of Murphys Law! (Read carefully the section on remote outback travel ...oh and BTW - the section on air lockers is a ripper - but I digress)

When a tyre fails on you you learn something - eventually you get a good run out of your tyres.
Just my experience for what it's worth.....
Kerry W (Qld)
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Follow Up By: The Bantam - Wednesday, Oct 29, 2014 at 13:35

Wednesday, Oct 29, 2014 at 13:35
Actually I do not believe the tech specs and the measurements go out the window in the bush......ya simply "can'a change the laws of phisics, Jim"

If the tyre fails...the tech specs will usually tell you why this has happened.

If the tech specs and measurements would have been heeded in the first place many of the tyre failures simply would not have happened


The single biggest problem with tyres on touring 4wds is.....people fail to pay attention to the tech specs and all to frequently run the tyres overloaded, under pressure or otherwise outside of the spec.

When you look at the tyres used on many 4wds.....they are being operated right up in the top end of their load range

take for example the factory 7.50R16 8 plies that come fitted to 70 series.
If a 70 series ute is loaded to capacity it is necessary and specified to run 65psi in the rear tyres......I have a set of dunlop road grippers in the yard off a new 70 series.....the maximum pressure stamped on the tyre is ...65psi.


So they are right at the very top of the load range and pressure.....in essence maxed out.

so they have to be run hard.

The tech specs and the measuremenst tell me that if a larger, higher rated tyre was used.......one that must have more air volume......it could be run at lower pressures.

Thus
less ground pressure....even when fully inflated to highway pressures
more latitude and safety margin all round.

now here is a thing many wont have observed......load V pressure performance of tyres is not linear.

In the middle of the load range load V pressure performance is pretty well linear.....but toward the top and the bottom of the acceptable load curve the performance gets non linear.

Up the top of the range more pressure is required to get an increased load capacity....at least that is my observation having graphed a few load tables.

So like everything.....if we want a tyre to work well and reliably, we need to be running it in the mid range of its capacity.

tyres natually have a self protecting mechanism.....when they get hot, the pressure inside the tyre increases thus tending to reduce the stress on the tyre......it balances and equalises.....unless you push things too far.

If you have a tyre running hard and right up at the top of its load range and iat its maximum pressure and still it is getting hot.....where has the tyre got to go but beyond the pressure spec.

The specs and the measuremenst tell us all this before we even turn a wheel.

The tech specs and the measuresurements confirm the experience not contradict it.

cheers
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FollowupID: 826991

Follow Up By: Ron N - Wednesday, Oct 29, 2014 at 15:25

Wednesday, Oct 29, 2014 at 15:25
There's another factor that comes into play in the complex equation between tyre pressures and loads and speeds - and that is, a tyre that is pumped up to a high pressure (say 65psi) has a reduced ability to absorb impact blows from gibbers, inbuilt rocks in the road surface, and other road debris, at speed.
You will suffer a larger number of "star fractures" and carcass damage with a heavily loaded tyre running at high pressure.

Thus, a bigger width tyre running at a lower pressure and with a higher manufacturers load rating, will perform better when it comes resisting impact damage at speed.

The downside to a larger tyre is that you vehicle will have a tendency to "float" more - and you'll really notice this, when you hit a deep puddle at speed.
Accordingly, there is a strong argument for increasing the size of tyres over standard fit, particularly if they have a higher load rating - but one has to keep in mind at all times, the precise effect that the larger tyre size has, on handling and steering.

Once you're alert to the alterations in handling and steering produced by larger tyres (steering more easily pulled off line, and "floatiness" on wet roads and hitting water/deep puddles at speed), then there shouldn't be any problems encountered by someone with adequate vehicle control skills.

The problems come when someone with inadequate vehicle control skills (young inexperienced drivers, and many women, feature here), drive vehicles with oversized tyres - then you immediately have a recipe for disaster, because they do not have the necessary vehicle control skills to cope with the alterations in handling and steering, created by the larger tyres.
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FollowupID: 826999

Follow Up By: The Bantam - Wednesday, Oct 29, 2014 at 17:36

Wednesday, Oct 29, 2014 at 17:36
Ahh but the truth of the matter is you have to go considerably over size to have any noticable problems resulting from increased tyre size.

In fact a vehicle with a modest increase in tyre size......one that brings it away from being right at the top of the load and pressure range may infact improve in every way....or in nearly every way.

If you are heavily loaded..hydroplaning is hardly going to be an issue, particularly if you are running open tread patterns....not at the speeds a 4wd is capable of anyway.

A slightly larger tyre that is now running at a lower pressure will conform better to the road surface and thus produce better traction.

likewise a tyre running at lower pressure..facilitated by running lower in the pressure range will also stay in contact with the road better than a hard tyre on rough surfaces.

In short running a modestly larger tyre will give all the advantages or airing down, while running at full highway pressure.

In addition a modestly larger tyre will require less pressure reduction to achieve a result off road because it already has a larger footprint.

here is an example

replace the factory 205R16LT in 6 ply that came on pre 05 hiluxes with 31x105R15 6 plies..which is a popular and practical change.

the maxed out load capacity of the 205 is 975kg at 50psi...unless you go to 8 ply when the load can go up to 1120kg but requires 65psi.

the 31's will do 1180kg in the 6ply with 50psi...maxed out...but it will be doing 975 kg at arround 45psi..still way above the rear axle limitations of that model.

so the practicalities of 31s on hiluxes is that you end up with 30% wider tyre than factory and arround 5 psi less pressure in the tyre..and a much larger safety factor.

If you keep your hilux light you can end up running 30 on the front and 40 in the rear with at least a good 10psi and 300KG per rear tyre spare load capacity.
running the same load on 205s and you would be running arround 45psi and only have 5psi and 100Kg up your sleeve.

AND in general hiluxes of that era do not run as close to the tyre spec as other vehicles like 70 series do.
The 70 series run right on the money for the rear axle limitations and the tyre capacity.

cheers
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FollowupID: 827010

Follow Up By: Member Kerry W (WA) - Thursday, Oct 30, 2014 at 01:54

Thursday, Oct 30, 2014 at 01:54
Quite correct Ron.
Bantam do you ever take a heavily laden 4WD for days over merciless roads in the middle of nowhere?
Kerry W (Qld)
Security is mostly a superstition. It doesnt exist in nature. Life is either a daring adventure or nothing.
-Helen Keller

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FollowupID: 827050

Follow Up By: The Bantam - Thursday, Oct 30, 2014 at 12:51

Thursday, Oct 30, 2014 at 12:51
What has that got to do with the facts.....I don't claim to be a hero.....can you articulate a sensible argument...produce some facts....or even offer a measured opinion on the matter.

There are hepas pf people who have "driven the simo" and know squat about anything.

Some of us manage to learn things without making the same mistake over and over.

As at stands, a great deal of what is said about tyres is nothing but superstision spread by those who simply don't understand why things fail.

NOTHING ever failed witout a good technical reason.

In the vast majority of cases 4wds and the tyres they are shod with fail because they are loaded and driven beyond their design intent.....design intents that are clear and easy to see if you have an inclination to read and under stand the specifications.

If someone is driving a vehicle loaded near to its, on road designed & specified load capacity and pushing it hard off road..expect breakages and failures.

Plenty of people are looking for reasons why their 4wds and the tyres they are shod with are failing in remote places......I don't have to have been there to know the reason.

But so many people simply do not want to hear that the vehicle is overloaded and not fit for the purpose they are putting it to......so they grasp at straws looking for any other solution but the one that should be obvious....and is clearly borne out by the technical data.

And they so often say........."you cant know because you have not been there"..........I don't need to go to the middle of the desert to know that a tyre loaded up to and beyond its specified ON ROAD capacity....then running reduced air pressure...in high temperatures ..and at high speed.....is sooner or later going to fail.

If I am to take any 4wd off road in any situation I want it to be loaded at least 25% to 30% below its rated on road capacity.
But people don't want to hear that.

cheers
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Follow Up By: Member Kerry W (WA) - Friday, Oct 31, 2014 at 00:41

Friday, Oct 31, 2014 at 00:41
Ah Bantam,

I notice that as this discussion has rolled along you now agree with what I originally said.

Well done!

Kerry W (Qld)
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Follow Up By: The Bantam - Friday, Oct 31, 2014 at 01:18

Friday, Oct 31, 2014 at 01:18
No I don't agree that technical specs and measurements go out the window.

Further.....what many many consider over spec and perhaps excessive may be barely within spec or even still overloaded....just not as badly as before.

If the specs are known and understood, they will show what is required.

Much less trail and error will be involved and Mr Murphy will be out of a job.


The problem lies with the notion of taking "heavily loaded" vehicles across heavy terain, under arduous conditions.



People need to grasp that the specifications laid down by the manufacturers in the way of load and towing capacities are for smooth improved surfaces ( made roads)....not off road use.

Reduce the load to 25% or 30% below on road rated limits and many of the leigon of failures will reduce dramaticly.

But that is a bit hard when you select a vehicle that has a total pay load of around 600KG and the bar work & racks weigh 200kg.

cheers
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Follow Up By: Member Kerry W (WA) - Friday, Oct 31, 2014 at 01:55

Friday, Oct 31, 2014 at 01:55
Yeah sorry mate - you got the wrong guy to preach to.

I had all this stuff sorted years ago.

Remember Im the one who "doesn't" have the problems you speak of.

...and pleaaaasse dont chase me for another reaction cause I dont have time I gave valuable feedback based on over 40 years of bush driving experience from the military to mining and just about everything in-between ... and No! I am not unscientific I did the research and kept records years ago - now I just know when I need to air down to 10 psi and when to run over 40psi.


Your comment above - "....can you articulate a sensible argument...produce some facts....or even offer a measured opinion on the matter"
....bantam dont assume things just because others are not interested in spending time justifying themselves.

You would be wise not to question others intelligence when you are so careless with your own spelling and grammar.


I have a double Major in science related subjects that are not relevant to this discussion. So I am pretty comfortable doing my own research on my passion for exploration and adventure when I have a problem to solve.

By discrediting others who contribute to this forum, or proclaiming that something is too good to be true - in your not so humble opinion, you can deprive some of the lesser experienced the accumulated wisdom this forum offers.

OVER AND OUT!




Kerry W (Qld)
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Follow Up By: The Bantam - Friday, Oct 31, 2014 at 09:17

Friday, Oct 31, 2014 at 09:17
This post has been read by the moderation team and has been moderated due to a breach of The Foul Language Rule .

Forum Moderation Team
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Reply By: rocco2010 - Tuesday, Oct 28, 2014 at 16:23

Tuesday, Oct 28, 2014 at 16:23
Gidday

While the pressure debate will always rage, there seems to be agreement that heat build -up is a major factor in destroying tyres.

A tour guide acquaintance of mine, who is a believer in reducing pressures, carries one of those infra red thermometer devices.

When the convoy stops for morning tea, lunch or whatever, it takes just a few minutes to walk down the line and check the tyre temps and he can quickly pick up who might be running a bit underinflated.

Just a bit more scientific than a hand on the tyre.

Also good to check the shockers after a run on the corrugations.

Cheers



AnswerID: 540985

Follow Up By: Ron N - Tuesday, Oct 28, 2014 at 17:07

Tuesday, Oct 28, 2014 at 17:07
What an excellent idea! - and I've got an infra-red heat gun, too - and checking tyre temperatures with it, is not something I'd have thought to do! They are quite accurate, too. Thanks for the tip, Rocco!

Cheers, Ron.
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Follow Up By: Member - Andrew & Jen - Tuesday, Oct 28, 2014 at 18:35

Tuesday, Oct 28, 2014 at 18:35
Hullo Ron
Different surfaces at the same temp will give different readings using an infrared temp gun. So it would pay to calibrate it with tyres so you can have confidence with reading.
Cheers
Andrew
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Follow Up By: olcoolone - Tuesday, Oct 28, 2014 at 19:47

Tuesday, Oct 28, 2014 at 19:47
?????? Heat is heat and the temprature is the same no matter what the material is...... Much like saying a liter of water is different in volume to a liter of oil.
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Follow Up By: Sigmund - Tuesday, Oct 28, 2014 at 21:09

Tuesday, Oct 28, 2014 at 21:09
As posted, those i/r guns only measure surface temps.
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Follow Up By: Member - Andrew & Jen - Tuesday, Oct 28, 2014 at 22:34

Tuesday, Oct 28, 2014 at 22:34
I will say it a different way
If you have a piece of stainless steel and a piece of rubber at the same temperature, my understanding is that an infrared thermometer will give you a different reading for each piece, neither of which is likely to be necessarily very accurate.
They will be in the ball park.
You need to apply a correction factor for each different material.
This advice was given to me by someone who uses infrared thermometers in laboratories.
Cheers
Andrew
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Follow Up By: Ron N - Wednesday, Oct 29, 2014 at 00:09

Wednesday, Oct 29, 2014 at 00:09
One has to bear in mind that rubber is a good insulator and a poor conductor of heat.
You can have a tyre that is much hotter on the inside of the carcass than the outside is reading.

Here's an eye opening video about heat buildup inside a truck tyre from welding on the rim, when the tyre is still inflated. A Big NO-NO!

Note the temperature reading is from the inside of the tyre.

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Follow Up By: Member - Andrew & Jen - Wednesday, Oct 29, 2014 at 09:13

Wednesday, Oct 29, 2014 at 09:13
Olcoolone

You might like to read the article in Wikipedia on emissivity and in particular, the effect of this property re instruments designed to measure the temperature of objects by thermal radiation.

The emissivity of various materials can be markedly different. For example, brick 0.90, polished copper 0.04, aluminum foil 0.03, paint 0.9.

My Infrared Thermometer is adjustable from 0.01 > 1.0. I leave it set to 0.9 as this covers most materials, even though not accurately.

Cheers
Andrew
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Follow Up By: fisho64 - Thursday, Oct 30, 2014 at 04:36

Thursday, Oct 30, 2014 at 04:36
"Heat is heat and the temprature is the same no matter what the material is...... Much like saying a liter of water is different in volume to a liter of oil."

Stick to arguing about what you know maybe?

As Andrew says-an infra red heat gun doesnt actually measure heat, it measured the infra red radiation, which is proportionate with temperature rise but varies due to surface emissivity of different material surfaces.

And in your very glib example, look closer and you may see that various liquids measured at a set temp will have a different volume at a changed temperature, maybe 1 litre at 20 deg, but each a different volume at say 0 deg
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Follow Up By: AlbyNSW - Friday, Oct 31, 2014 at 07:49

Friday, Oct 31, 2014 at 07:49
As often happens here the point made gets lost in the bleep contest
Is it really that important the differences between heat and different materials and volumes blah blah blah?
The point made is that the guy uses his temp gun to check changes in temp from a reference point
Surely that is better than the hand heat test? Why can't you just leave it at that and take it as a great idea
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Follow Up By: Ron N - Friday, Oct 31, 2014 at 13:28

Friday, Oct 31, 2014 at 13:28
I have a moderate-cost, Taiwan-made infra-red heat gun, with no calibration capacity.
It gives a good general indication of SURFACE temperature, as indicated by the infra-red radiation emitted from the object I'm measuring. It's not a lab instrument.

I can't lay my hand on the paperwork for it at present, but I seem to recall the accuracy range is around plus or minus 2%. That's good enough for general field purposes.

You can buy very expensive IR heat guns with emissivity calibrations built in, with inbuilt data-logging capabilities, with different types of thermocouples that have differing and increasing sensitivities.
It all depends on how much you want to spend, and how accurate your temperature-measuring has to be.

The main factor involved in using IR heat guns is understanding how the emissivity of the object you're assessing, performs in emissivity ratings - and how the distance you hold the gun from the object you're assessing, affects the temperature reading.

Rubber has an emissivity rating of .95 - meaning it is an excellent material for absorbing reflected IR energy and only emitting its own IR energy.
Generally, the closer a material’s emissivity rating is to 1.00, the more that material tends to absorb reflected or ambient IR energy, and emit only its own IR radiation.

Cheers, Ron.
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Reply By: Member Kerry W (WA) - Tuesday, Oct 28, 2014 at 20:02

Tuesday, Oct 28, 2014 at 20:02
If this is of any use - from my personal experience..
Never have had issues with sidewall or tyre failure by lowering pressure. I generally use higher and wider tyres, have trialled most brands. I do however monitor my speed and tyre temperature. Avoid towing anything in remote areas. I never buy cheap tyres. I look at how my tyres bag out for the conditions and go from there.

IMHO there is a certain degree of gut feeling/nouse/experience required to set up the vehicle in the first place and run it on harsh surfaces. EG I ask myself "Does that look right ? Maybe I overspend or over specify but whatever it is it works.
Sorry can't add more but do see a lot of big heavy vehicles on smallish looking tyres (to my eye) having tyre problems. It is a bit of a black art and from what I read here I must be an exception cause I often use even lower pressures than stated in many of these replies and seem to have reliable tyres. My only suggestion - Go bigger and if you can and buy tyres suited for your worst case off-road scenario. Don't overload them - If they don't look tough enough for the job then maybe they aren't.
Kerry W (Qld)
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AnswerID: 540996

Reply By: tommo05 - Tuesday, Oct 28, 2014 at 21:04

Tuesday, Oct 28, 2014 at 21:04
With regards to tyre manufacturers, it is worth noting that for legal reasons they will ALWAYS tell you to run them at their recommended pressure for the load you are carrying. These recommended pressures however do not take into account road conditions.

To my knowledge Cooper Tyres are the only manufacturer that acknowledge the lower pressures argument. Not sure though what their take is on corrugations.

This is pretty much the oldest 4x4 argument in the book. Experiment and stick with what works for you. I have only had to replace one tyre in the past 10 years, and that was a sidewall that got spiked at 40 PSI. For the record I reduce to 30 PSI for corrugations, because that is my personal preference.

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Follow Up By: tommo05 - Tuesday, Oct 28, 2014 at 21:18

Tuesday, Oct 28, 2014 at 21:18
Oops when I say I have only had to replace one tyre, I mean I have only had one failure. Obviously I have had a few new sets of tyres in 10 years!

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Reply By: The Bantam - Tuesday, Oct 28, 2014 at 21:50

Tuesday, Oct 28, 2014 at 21:50
There is a lot of mis-understanding over tyre pressures.



The first thing that must be understood is.....if you are running at highway speeds, you need to be running highway pressures......regardless.




That means at least minimum inflation pressure for the load carried as found in the tyre standards manual or in the manufacturers specs.

80KPH is pretty much highway speed...the lower end of highway speed...but highway speed all the same.





The second thing that so many fail to grasp is.....the minimum normal inflation pressure varies for the load carried and the tyre fitted.

AND...it can vary quite a bit as the load varies.




If you have not weighed your vehicle ready to travel and looked at the load V pressure tables for the specifc tyre you are running......frankly.........you have no idea what pressure you should be starting with.


Combine the above with the fact that many touring 4wds are overloaded on one or both axles..........but the owners are completely oblivious to the fact.



Then there is the whole idea of airing down.........the whole idea and concept revolves arround low speed 4wding over various ground types and for relativly short periods.

You woud get away with running pressures well below the tyres ability to carry long term if you where not doing so hour after hour day after day...and in hot conditions.

It may be well and good to drop pressures considerably when traveling at low speeds and for relativly short distances......but once the speed and duration gets up...you realy need to think about how much if at all you reduce your tyre pressures.

If you where starting arround 40psi for highway work it may be suitable to reduce to 30 psi for generall off road and 20PSI in soft sand.......IF you are traveling in low range or in lower gears in high range.........AND at relativly low duty cycles...

some off road trips may work out to be less than 100Km in reduced tyre pressures over a weekend.....a trip up the beach may be a couple of hundred Ks..all week end.

so.

just for an eye opener

here are the tyre load limits at cold inflation pressures for the 265/75R16 light truck tyre from the standards manual.
figures in psi converted from kpa to the nearest 1psi

890kg at 36psi
1010 kg at 44psi
1120 kg at 51 psi
1240 kg at 58psi
1360 kg at 65psi
The table goes further but very few would be using thres capable of running above 65psi.
The table is fairly coarse in this group of tyres, but if you graph the figures provided you can work out what is in between...just remember the grap wont be all linear.


so at 36psi....the rear axle loading should be less than 1780Kg...consider the maximum rear axle loading on a 70 series is arround 2300kg...you would have to be arround half a tonne under under GVM to run that pressure in the rear long term.
BTW...toyota commercials are designed to carry the majority of the payload on the rear axle.

The other thing to consider is that at 2300kg, the maximum rear axle loading is near the maximum load capacity of the tyre....at 65psi.

There would probably be more latitude for pressure reduction if the tyre was running in the lower part of the load curve.




There are a lot of well meaning comments about tyres.......but untill the rig is actually weighed.....as it travels with all aboard..AND..the load V pressure tables referenced......big chunks of it mean nothing.

All to often people have the tyre pressures wrong, even before they start talking about airing down.

cheers


AnswerID: 541009

Follow Up By: The Landy - Wednesday, Oct 29, 2014 at 07:51

Wednesday, Oct 29, 2014 at 07:51
I have come to the same conclusion over time.

Cheers, Baz - The Landy
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Follow Up By: The Bantam - Wednesday, Oct 29, 2014 at 09:56

Wednesday, Oct 29, 2014 at 09:56
Here is a bit of background that may help illustrate the issue.

Back in the 60's and 70's when radial ryres where just comming in many of the manufacturers where specifying two different recommended pressures...one pressure for round town and a slightly higher pressure for highway work.....I think a lot of this was due to the perception that radial tyres rode harder and where noisier than crossplies....AND people realy toock time to get used to running tyres as hard as radials needed to be run.
A car running crossplies in the mid 20's would be running similar sized radials in the mud to high 30's...properly inflated

Arround that period there where a lot of problems with radial tyre failures...sure some of them where due to piss poor construction.....but a lot of them where clearly identified as being due to under inflation.

These days all car manufacturers are specifiying one tyre pressure for all on road uses.

I was tying to dig up an image of a 75 series tyre plackard...but none came up on google.
BUT someone had posted up a page image from a 70 series manual.

now this is interesting
I'd post the image....but I cant on this forum.
here is a link
http://forum.ih8mud.com/threads/just-how-slow-are-hzj75-with-2h-engines-%E2%80%9Cnon-turbo%E2%80%9D.398153/

for the FJ75 running the stock 7.50R16 8 ply light truck

For normal use...above 80kmh..they recommend 34psi front and 65psi rear....but wait there is more below 80kmg for " sand driving" they recommend ...wait for it....31psi front and 61psi rear.

One assumes fully loaded.......yeh ..grain of salt....conservative engineering and a risk averse public liability outlook.

BUT

That is a pretty small pressure reduction they feel confident with.

Remember too that the 7.50R16s even in 8 ply will be running very close to their capacity in this application.


As for tyre shop pressure recommendations.....as have been mentioned below.

HELL.....do not trust any tyre shop to recomend tyre inflation pressures...they simply have a very long and consistent record of getting it wrong and making generalisations that are wild and don't hold true.

We hear a 40psi front and 50psi rear recommendation mentioned

well

from the toyota recommendations if it was a FJ75 running most tyres the fronts will be too hard and if fully loaded the rears could be as much as 15psi under inflated.

seriously...ya gota weigh it and look at the tables......or at least at the tyre plackard if you are running factory stock tyres.

cheers
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FollowupID: 826966

Follow Up By: The Landy - Wednesday, Oct 29, 2014 at 12:27

Wednesday, Oct 29, 2014 at 12:27
In terms of weight, it isn’t too hard to establish what the base is and compile a load chart so you know exactly how the vehicle is loaded at any point of time.

I use the following, and whilst I don’t have a chart to determine individual axle weights as it is far too complex to assign moment arms to the load chart, the individual axles have been weighed in “touring mode” to ensure compliance.

It is worth noting that the rear axle weight is the limiting factor for loading, not the GVM. As it stands I could not load to maximum GVM due to rear axle limitations.

And on tyre pressures, the vehicle has a GVM of 3,900kg after the installation of a Lovell’s GVM upgrade suspension kit. The tyre pressures based on the revised GVM follows, but in summary in our touring configuration (loaded to around 3,500kg) the suggested pressures are 38psi front, and 69psi rear.





Cheers, Baz – The Landy
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FollowupID: 826986

Reply By: Member - eighty matey - Tuesday, Oct 28, 2014 at 22:24

Tuesday, Oct 28, 2014 at 22:24
G'day Rosco,

we did a Kimberley trip similar to yours a couple of years ago.
We were running Dick Cepek FC11s. I was dropping and raising pressures whenever we changed surfaces. The rear tyres were stuffed when we finished our 13,500 kms and one front one didn't make it back along the Tanami.

I spoke to a few tyre blokes - Bedourie, Cunnamulla, Borroloola, Mt Isa, here - and they all say they don't touch the tyre pressures unless they're in sand. All of them.

Last month we were in Qld and NT, a lot of dirt roads, same load, same vehicle, didn't touch the pressures. No catastrophic failures, two stakings in the tread, some chipping but nothing like the Kimberley trip.

Speed is an important factor but different brands also vary greatly. I monitor the tyre pressures with tyre dogs. I played around with cold pressures a bit early in the trip. Whether I started with 40, 50 or 60 in the rear they still went up 10 psi in the first hour on a variety of surfaces and pretty much stayed there.

I took the advice of the tyre guys and had a minimum of 40 psi front and 50 psi rear, unless we were in sand or rock crawling.

I probably haven't answered your questions but I hope I helped a little.

Steve

AnswerID: 541013

Reply By: Member - bungarra (WA) - Wednesday, Oct 29, 2014 at 17:20

Wednesday, Oct 29, 2014 at 17:20
"quote I ... like most here, have been a great believer in reducing tyre pressures when traversing corrugated/rough dirt roads..end quote."'

I have never subscribed to lower presses on hash / rocky/ corrugated roads.....I have travelled those roads you mentioned and many more in harsh rocky goldfields country as well and always maintain high pressures that is > than 50pis Always I have been very heavy as well.......The tyres have mostly been BFG or Coopers.

My reasoning is simply the lower the pressure, the greater foot impint (hence the reason for low pressure in sand)
The side walls also bulge making them more susceptible to side wall damage from rocks...the tyre flexes more generating heat etc.

I wont change my view based on my experience and many km's doing this........I do however, control my speed and am very conscious of nurturing the suspension and not using the tyres as the cushion

The picture of the side wall bulge looks to me like heat generating from over loaded ( there are 2 different specs for BFG ...look closely as its not easily apparent)....or under inflation or both
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AnswerID: 541045

Follow Up By: backtracks - Wednesday, Oct 29, 2014 at 20:09

Wednesday, Oct 29, 2014 at 20:09
Too much weight and too much speed are the main tyre killers IMO. On the ab highway I ran around 21f and 24r cold.Speed around 30-40 k/hr untill WA side, then up to 80 k/hr at same pressure ( yer perhaps too low !) 3000kg all up. GQ wagon. No tyre problems. BFG all terrains.
Googs track 18 and 16 hot.
Baladonia track-quite rocky in places- 16 PSI.
All around 2700 kg. No puntures.
Noticed the higher the tyre pressure the hotter the shocks.
Nothing will convince me that higher tyre pressures are better- with my speed and weight.

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Reply By: 671 - Wednesday, Oct 29, 2014 at 23:09

Wednesday, Oct 29, 2014 at 23:09
Geez after reading all of this it is wonder I don't have a headache. All I can say is thank heavens I have stuck with stock size 205Rx16 LT tyres and tubes on factory pressures of 25 front at all times and 25 to 34 rear depending on load. There have been no problems at all over a seven year period everywhere from Blue Rag, to the Gunbarrel to the Sydney Harbor Bridge. I reckon Toyota got it right when they specified those tyres at those pressures and the tyre manufacturer told me not to change a thing.

If I had a Cruiser instead of a Lux, it would be a 7.50x16 on factory pressures and I am sure I would get the same results.
AnswerID: 541065

Reply By: Sigmund - Thursday, Oct 30, 2014 at 06:36

Thursday, Oct 30, 2014 at 06:36
So, we have samples here of folk who don't air down on corro, gibber or other rock, and those who do. Assuming we're comparing apples with apples we can conclude that tyre pressure doesn't matter that much except on sand and then only for traction.

Without rereading the whole thread there's only one first hand report of failure. The data in the OP is a bit limited though. The weights were estimated not measured.

So it it may be fair to say that it wasn't due to pressure but to something else. Dud tyres? Overloading? Factor X?

...

For myself, I'll take the advice of the roadhouse mechs I've spoken to for who this stuff is their bread and butter and continue to air down. Have done that over three outback trips on two varieties of LT construction keeping under 80 with no failures or chipping out. Less chance of staking, a smoother ride over corro and much better grip on sand and gravel.
AnswerID: 541068

Reply By: The Landy - Thursday, Oct 30, 2014 at 08:36

Thursday, Oct 30, 2014 at 08:36
An interesting topic that highlights differing approaches by many.

What it tells me is that it is a “trial and error” scenario and that there is no one size fits all approach.

Those that air down perhaps have sufficient evidence to suggest it is the best way to go, others who don’t might also argue the same based on their own individual experiences…

Perhaps it is a bit like the “shoo roo” whistles on the front of some vehicles. If you have one and never hit a roo you can argue they are most effective; if you don’t have one and haven’t hit a roo, you might be entitled to suggest they are not worth the money. But neither scenario tells us much unless it has been tested under controlled conditions over a long period.

I suspect the tyre argument is much the same, remembering that changing one thing, or nothing at all, usually has impacts on other areas, and not always in a positive way…

Deflating or not deflating tyres will have benefits and drawbacks.

But plenty of food for thought in this post and it has given me some things to research and think about – and that is what this forum should be all about!

Cheers, Baz – The Landy
AnswerID: 541073

Reply By: Member - Rosco from way back - Thursday, Oct 30, 2014 at 13:01

Thursday, Oct 30, 2014 at 13:01
It would appear I have opened a can of worms here and a tad more than I bargained for.

A shame it would appear reasoned sensible debate must be coloured with that which approaches invective and is, in my opinion unnecessary and uncalled for.

AnswerID: 541078

Follow Up By: The Landy - Friday, Oct 31, 2014 at 08:14

Friday, Oct 31, 2014 at 08:14
Rosco


If you wade through the posts there is some “food for thought” amongst the noise, I’ve noted a couple of things to think about and that is what makes the forum worthwhile…

It is subjective topic and therefore views will range from those that do, those that don’t, and those who are in between.

Cheers, Baz – The Landy
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Follow Up By: Member - Kevin S (QLD) - Friday, Oct 31, 2014 at 12:24

Friday, Oct 31, 2014 at 12:24
Discussions on these types of subjects are a bit like debate in Federal Parliament, Rosco. Everyone speaks from a predetermined position and no one is convinced to change their mind. The greatest beneficiaries of this debate are probably the readers who did not participate.

I read it all with interest but I know what works for me and that is what I will keep doing.

However, what ever the inflation level of the tyre, I believe the greatest damage comes from excessive speed. My motto is "Never over 80 on an unsealed road". And mostly well below.

Cheers,

Kevin
Kevin
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Follow Up By: Member - Rosco from way back - Friday, Oct 31, 2014 at 12:36

Friday, Oct 31, 2014 at 12:36
I agree Baz and Kev.

If you care enough and have the patience to sift through the dross you may be lucky enough to come across a small gem of wisdom.
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Follow Up By: Steve in Kakadu - Friday, Oct 31, 2014 at 12:37

Friday, Oct 31, 2014 at 12:37
"The greatest beneficiaries of this debate are probably the readers who did not participate."

Yep you got that right, I have used my methods of tyre inflation for 35 plus years and won't change, but I am not going to tell anyone here because half of you will believe me and half of you wont.

Just sayin LOL
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Follow Up By: andrew t - Sunday, Nov 02, 2014 at 21:29

Sunday, Nov 02, 2014 at 21:29
we did the gibb in the prado and camper trailer this year coopers on the camper and toyo open country at11's on the prado. about 42psi on the bitumen and about 30psi ish on the gibb gravel . no probs with any of them and ride was ok and that was just our little trip from melb to the gibb and home over 17,000 kms travelled and no tyre probs at all.
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FollowupID: 827289

Reply By: get outmore - Saturday, Nov 08, 2014 at 00:09

Saturday, Nov 08, 2014 at 00:09
first time I travelled the Kimberly I ran 50 psi in the tyres and barely made it to kunununurra with 2 wrecked tyres and one leaking one.
just recently I returned after having my wagon in the Kimberly for 5 months doing trips from kalumbaru. to kakadu and everything in between.
I had the cheapest tyres money could buy. road stone roadians and ran low pressure low speeds for the tracks.
I lost one after slicing a sidewall after not re inflating after going to 10psi to get out of a bog
besides that yes there chipped but after many of the rocky tracks all tyres were covered in sidewall scuffs but there still fine
AnswerID: 541411

Reply By: Sigmund - Sunday, Nov 09, 2014 at 16:48

Sunday, Nov 09, 2014 at 16:48
Here's a thoughtful piece that I think is worth a read:

http://outbackjoe.com/macho-divertissement/macho-articles/tyre-pressure-guide/
AnswerID: 541457

Follow Up By: AlbyNSW - Sunday, Nov 09, 2014 at 20:00

Sunday, Nov 09, 2014 at 20:00
Have a read of his tyre pressure graph
22 psi = max speed of about 2kph
And 0 kph at 20 psi
0
FollowupID: 827565

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