a plea - let your damn tyres down!

Submitted: Wednesday, Sep 04, 2002 at 00:00
ThreadID: 1911 Views:2582 Replies:8 FollowUps:7
This Thread has been Archived
Having just done the Simpson and experienced severe corrugations on dirt (comfort ok in a Disco, but hell on tyres and suspension) and chewed out approaches to sand dunes, I feel there is an urgent need for high-profile education of 4wdrivers re tyre pressures. This education needs to come through forums such as this website, 4wd mags, 4wd clubs/associations, National Parks and road authorities (large signs recommending pressures be reduced from bitumen levels for dirt/sand).

This is particularly the case given the rapid increase in people buying new 4wds who have little 4wd experience; although it is amazing how many 'experienced' 4wders have little knowledge of appropriate tyre pressures or are too lazy to let them down and/or too tight to buy a decent compressor. 'Low' tyre pressures means low. It is interesting to note that the Simpson recovery vehicle (Cruiser trayback) runs 25psi on rough dirt and 10psi in the sand. These pressures may be a bit low for some and clearly depend on vehicle, load, tyre type and driving style (I run 12-18psi on sand and 25-30psi on dirt in Disco). However, some people clearly think that 'low' pressures in sand are 25-35psi and don't even know about the need to reduce pressures on dirt.

So...please...let your pressures down! Trust me, it will be easier (and cheaper) on your tyres, suspension, vehicle, luggage, occupants, fuel bill...and roads and therefore other users!
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Reply By: pathfinder - Wednesday, Sep 04, 2002 at 00:00

Wednesday, Sep 04, 2002 at 00:00
PostScript to the above: Whilst in the Simpson we met a large group coming the other way, all in new, fully decked out (overloaded) Cruisers and Patrols. We picked up their UHF Channel and were privy to the leader berating someone further back for being bogged indicating that they should know how to drive in these conditions. It turned out that the leader was an Opposite Lock tag-along vehicle and that most of the group were running high tyre pressures (as well as very top-heavy roof rack loads of up to 8 Jerries). A member of our group, ex-ranger of the Simpson, told the group via UHF of the need for low tyre pressures. This was met with silence. So much for the benefits of joining a tag-along tour where the organisers will make sure you have knowledge before you leave (e.g. vehicle set-up, correct loading etc) as well as whilst on tour. I would have thought it is the responsibility of such tour leaders to make sure that vehicles (usually owned by inexperienced 4wders) are set up properly and running correct tyre pressures. I don't think it is exactly a positive first experience to be criticised publicly by someone you are paying for something that is due to poor instruction rather than personal fault.
AnswerID: 6351

Follow Up By: Member - Trevor - Wednesday, Sep 04, 2002 at 00:00

Wednesday, Sep 04, 2002 at 00:00
It's funny you should mention Opposite Lock and the "Tag Along Cowboys." We were in the Simpson last year and the same happened. This time they were in such a hurry they couldn't/wouldn't help a young bloke (visitor to Australia) bogged. They were too busy geting bogged themselves and driving like madmen. They didn't bother to talk to us mere mortals. The leader was more interested in keeping his shirt clean.
Finally some real Australians helped the young bloke out. There were many people we spoke to in the Simpson who would not let their tyres down. There was a correlation between those who did let their tyres down - they were to people who stopped to have a chat. Maybe road spikes at each end would get the message through! Listening to conversations at Birdsville (while gettying a trye repaired) no one understood about using lower pressures for dirt roads. Those city pressures make it really rough for others as well. Maybe we should give out stickers for those drivers who do the right thing. Maybe Paul Keating could put a Pox on all those with high pressures in the dirt and sand.
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FollowupID: 2818

Reply By: royce moncur - Wednesday, Sep 04, 2002 at 00:00

Wednesday, Sep 04, 2002 at 00:00
Fair enough....lower tyre pressures on loose dirt/bulldust. But be careful. Harder gibber, clay, roots [Frazer Island] this may not be as appropriate. Driving style might be the more important factor. I don't think that it is cheaper on tyres though. The sidewalls suffer. Speed is more important. The right speed for the conditions. Do you reckon that the corrugations are caused by high tyre pressures. I got that impression. Cheers Royce
AnswerID: 6374

Follow Up By: Kezza - Thursday, Sep 05, 2002 at 00:00

Thursday, Sep 05, 2002 at 00:00
Despite much debate re creation of corrugations primary cause is loss of traction of one or more wheels along with the pothole effect. Vehicles with LSDs create far fewer corrugations than those with open diffs but you will never stop them developing as long as people have heavy foot. Tyre pressures will affect the degree of traction and hence axle tramp but once the initial bumps of a corrugation develop they just get worse because of the impact of the tyre as it hits the valley of the corrugation. The main factor then becomes the speed of the vehicle. The damaging effect of the trye conforming (or not conforming ) to the corrugations at various pressures will change with speed. (Read that last bit twice)
happy shaking,

kezza
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FollowupID: 2827

Follow Up By: Pathfinder - Thursday, Sep 05, 2002 at 00:00

Thursday, Sep 05, 2002 at 00:00
Royce - it is a common misconception amongst tyre retailers that low pressures are the sole cause of sidewall fracturing. However, these people usually have no experience of offroad situations. Even on rocky roads, the recommendation of people in the know is to reduce tyre pressure so that tyres conform better to the surface to avoid punctures and sidewall fracturing. Even at 25psi, most tyre sidewalls (particularly LT type) are upright enough to avoid sidewall punctures.
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FollowupID: 2838

Reply By: Mal58 - Friday, Sep 06, 2002 at 00:00

Friday, Sep 06, 2002 at 00:00
Pathfinder,
Tyres and tyre pressures always seem to be hot topics on any 4wd forum. With regard to appropriate tyre pressures, when we were on Fraser Island 2 years ago, we were talking to the local ranger and not having much experience driving in sand (being a Victorian) I wanted to check I was doing the correct thing with tyre pressures. (I had let them down to 20-22 psi cf "normal on road" of 34-36 psi). The ranger was a bit "reluctant" to formally advise, because, he was concerned about the legal implications. If he advised a low trye pressure, and we subsequently had an accident because a tyre rolled off the rim, then he felt he would be liable if we subsequently sued.
He did agree though, that the use of high tyre pressures does chop up tracks and cause deep ruts, but then again of Fraser Island, one decent rain, and the sandy tracks are flat again.
I think, that user education is something that needs to be done.
Rgds,
Mal58
AnswerID: 6427

Follow Up By: Member - Mal - Wednesday, Sep 11, 2002 at 00:00

Wednesday, Sep 11, 2002 at 00:00
Mal58, If you want to find out what pressure the rangers reckon is correct, don't ask what they reckon, ask what they run in their vehicles. On Moreton Island they run their Landcruiser traybacks at 11-12psi. That way they haven't made a recommendation. Mal Try.
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FollowupID: 2935

Reply By: royce - Saturday, Sep 07, 2002 at 00:00

Saturday, Sep 07, 2002 at 00:00
Even though I've been driving a couple or few decades, with a fair bit off road, I don't reckon I know everything. However my experience is this. After a week on Frazer island where I deflated my tyres to around 20 psi ... I think 'cos it's a long time ago.... I had three of my tyres crack the side walls over the next few months. It has never happened since or again! Here's the thing...... I have a farm, live on a dirt road and drive down some fairly rough tracks. Yeah a lot of the time on the black top, but plenty of times across a soggy paddock or sandy ridge. The idea that you 'must deflate your tyres' is a bit dodgey. I reckon I saw plenty of locals travelling along the Tanimi Track a couple of years ago, who didn't worry about deflating tyres. I certainly wouldn't worry about deflating them for an hour's trip down a bit of bull dusty or sandy stuff. The idea that a softened tyre will for better to the shape of the road and corrugations is a nice idea. hmmm well it would be very marginal unless you travel at 10ks an hour. If you are moving at anything over 30 ks it would make almost no difference.... okay.. tell me I'm wrong. I think maybe the case is being overstated. By the way. I WILL from now on deflate my tyres a bit more than I would have done on the advice of you blokes. By the way do you watch Russell Coight?? Damn near me! But then again, I bet we have all done some of his 4wd antics....Cheers Royce.
AnswerID: 6460

Follow Up By: Pathfinder - Monday, Sep 09, 2002 at 00:00

Monday, Sep 09, 2002 at 00:00
Royce - all I can put your Fraser Island experience down to is bad luck or bad tyres - 20psi definitely isn't too low on sand and 18psi would probably be even better (or even 12 psi if you have a light vehicle). The roads I'm talking about are not soggy paddocks or sandy ridges nor sandy tracks like the Tanami. They are hard, rocky gibber plain jobs and if you don't deflate your tyres, you will fracture a sidewall and/or incur a puncture. There is no risk of your tyre separating from the rim at 25 psi even at reasonably high speeds (80kph) unless you corner or brake extremely suddenly.
0
FollowupID: 2892

Reply By: Revs - Monday, Sep 09, 2002 at 00:00

Monday, Sep 09, 2002 at 00:00
For what it's worth.. Having travelled "many many" times through Outback NSW and Q'land, I feel I can add my "two Bob's worth" With regard to steel belted radials of std size,ie 750x16. My experience has been as follows. Driving on rough stony country and Gibber plains, I have NEVER had a puncture or a damaged sidewall, with the tyres inflated to 35psi. However, I do DRIVE the vehicle with constant vigalance, looking for and dodging, large stones etc that are in the path of my vehicle. I also match my speed to the condition of the road. The corragation debate rages and I wish to put my "bit" in. Corragations are a function of the natural frequency of the vehicles suspensions that pass along the gravel road. You will notice that corragations caused by trucks are further apart that corragations formed by cars and 4WD's. Tyre pressure would have some effect to the severity (height) but not the pitch (distance apart).
AnswerID: 6490

Follow Up By: Royce - Wednesday, Sep 11, 2002 at 00:00

Wednesday, Sep 11, 2002 at 00:00
You see, I have this probem. What sort of dodgy four-wheel drive tyre is it that needs to be deflated so that the sidewalls touch the ground? Surely there must be a tyre that is run at a normal pressure in these roads? What do the tyre manufacturers recommend? Do they say "distort our tyre so that they are nearly flat, the next time you drive 500 ks of outback road"? I just puzzles me that rough and tumble rocky old roads need to have nearly flat tyres. Sand dunes and beaches yes. Hmmm I'm confused. I have to accept that the experienced people on this forum say to deflate, so I probably will... Cheers Royce
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FollowupID: 2942

Reply By: Revs - Thursday, Sep 12, 2002 at 00:00

Thursday, Sep 12, 2002 at 00:00
As allways, there is the "pinhead" element that goes off on a tangent, expounding all their "pet" theories on all aspects of 4WD's etc, AND, trying to convince the public of their 4WD experience! To go on about the effects of tyre pressures and how this relates to corrugations is a bit "rich"! EACH and EVERY vehicle has it's own criteria regarding the ideal pressure in the tyres. Tyre SIZE (width) is especially important, along with the profile of the tyre ie; distance from the rim to the ground, where low profile tyres will be a "liability" in rocky country, and sidewall damage allmost certain. In sand, the "bagging" beneficial effect of tyres run at a low pressure, is well known. But, in stony country, the reverse is the case! Howeverin my experince, I am referring only to relatively narrow section, radial tyres. NOTE.A wider section tyre will have more chance of being damaged with the tyre inflated at high pressure, and probably should not be inflated to high pressures in stony country.(the balance is hard to achieve). The next time you venture into Gibber or stony country, stop and inspect the sidewalls of your tyres, especially the shoulders. If you are running yours tyres underinflated, then you will notice that the shoulders of the tyres will be "marked" or even "nicked" by the bulge of the tyre being exposed to the surface of the road. Ultimately it's your decision. But my advice is to err on the side of higher pressure.
AnswerID: 6563

Follow Up By: Pathfinder - Friday, Sep 13, 2002 at 00:00

Friday, Sep 13, 2002 at 00:00
Thanks for that enlightened feedback 'Revs'. Unfortunately you are guilty of what you are accusing others of - i.e. 'pet theories'...does this make you a 'pinhead' as well (not a particularly constructive description is it 'Revs' - great username by the way...). The purpose of these forums should be for people to share their experiences in an amicable fashion. I understand this website will soon be posting definitive advice from an off-road tyre expert (i.e. versus a city tyre retailer). In the meantime, all people like myself can do is go on our own experiences and discussions with people who actually live in these locations which on a recent trip were as follows: the only vehicles on our trip to have tyre blowouts were running higher pressures; and, locals were running 25-30psi on rocky roads with light truck type tyres. You will note in my original posting that I didn't specify precise tyre pressures as I am well aware that it depends on tyre type and GVM.
0
FollowupID: 2958

Reply By: Revs - Wednesday, Sep 18, 2002 at 00:00

Wednesday, Sep 18, 2002 at 00:00
4WD Tyres



What pressure do you put in these damn things?
Most of us probably ask ourselves this question as we try and fit the bent mangled service station doohickie that never seems to seal first try onto our tyre valve and press down the lever. It’s a good question and one I’ve never heard a definitive answer for. Of course there is no definitive answer for any category of tyre but I’ll do my best to shed some light on this shadowy subject.

First up, we have to grasp the concept that the amount of air we squirt into a tyre should be proportional to the size of that tyre and load applied to it. It is the internal air pressure that supports that load and allows the tyre to perform its intended function. Picture the tyre on your racing pushbike if you cut a section as long as your finger out of it. If you looked at it end on, its section thickness wouldn’t be much more than that of your thumb. If you could seal the ends and pump it up to 20 psi or 136.2 kPa you would find that you could crush the thing flat with your thumb and forefinger. Now go outside and cut the same section from your neighbour’s fat tyres on his Pajero (only kidding) and you’ll see it has the sectional thickness of a watermelon or thereabouts. Pump this up and try to crush it and you’ll need a hydraulic jack. This is a function of the physics of force and how it applies to cross-sectional areas. This is why your racing bike needs 70 psi and your car probably needs half that.

Now, if I haven’t confused you too much, how does this relate to your buckin’ and bouncin’ Hilux you may ask - as someone told you that 38 psi would do the job admirably. Well, it would on a heavier machine but assuming yours has been fitted with the almost standard after market fitment of 31 X 10.5 X 15 Desert Duelers or BFGs – its going to kick and jump around. The standard factory fitment for the Hilux utes was a 205R16 that was about an inch and a half shorter and 4 inches narrower. You have a much bigger tyre on a relatively light vehicle so the tyre pressures could easily come down to 26 – 28 psi. Now if you fitted the same rubber to an 80 series Toyota with its extra 600 kg mass and about triple the horsepower you’ve got a different situation altogether. The tyres would bulge and the car would ‘lurch’ on the corners as the sidewalls wobbled. If it were my machine another 10 pound would be added straight away maybe even 14 to make a 40 psi (272.4 kPa) total to get the machine to handle safely and enjoyably.

During my years of safety training we did a fair bit of driver training in sedans and 4WDs. The instructor we used a lot was a true gentleman by the name of John Van Leeuwen who runs Drivesafe Australia in WA and is an accomplished kart and Formula Ford state title holder. He loves his machines and understands the mechanics of them better than most. He made no secret of the fact that he likes people to err on the side of pumping their tyres up to the upper end of the manufacturers recommendations. After participating in many of the driving courses most of us got to dislike the heavy steering and sloppy handling of under inflated tyres and found it harder to modulate the brake pedal to achieve an emergency stop.

There is also the matter of tyre wear that increases with under inflation. To give you an idea of why tyres wear out with every day use – stand back and have a look at the round black things on the rims of your car and… you’ll notice that they’re not exactly round. Where they touch the road is flat and the sidewall bulges out noticeably at this point. If you were to let more air out of your tyre the flat section would get longer and the bulge bigger. As you are bowling down the road your tyre tread and sidewall are continuously bending and flexing and, where it meets the tar, rubbing against the road. This generates an enormous amount of heat which is the sworn enemy of tyre wear and degradation. If your heat a tyre up enough you could peel it apart with your hands. This flexing is the reason why manufacturers of tyres and cars recommend that you increase tyre pressures by 4 psi or 28 kPa when you are going on a trip to the country (or loading up your rig).

So what do we do about pumping up our tyres? I personally start with a median tyre pressure of 35 psi and work my way up or down from there depending on the situation that I’m faced with. If your interested – and most motor enthusiasts are – I’d follow a 5 step plan and add your own personal fuzzy logic factor just to make it more interesting. To add a personal touch, I’ll relate the logic to my work truck, which is a Patrol king cab GQ with 16 X 8 wheels and 265/75/16/ BF Goodrich Mud Terrains.

1. Tyre Size – Are they generally a large tyre in relation to what similar vehicles wear? Are they larger than what is on the tyre placard for that vehicle? Yes and yes – I might drop them to 33 psi.

2. Load – Is the vehicle loaded/heavy, likely to carry a load or tow a trailer in the near future? Nope, but it’s a 6 cylinder diesel and they are traditionally nose heavy – I might bump the fronts up to 35 again.

3. Speed – Are highway (freeway?) speeds likely? Are we in the middle of a warm season that will make the flexing heating problem worse? Yup yup – I’d better whack the drivers and steerers up to 38 all round.

4. Tyre Rating – You have to admire the quality tyres like BF Goodrich and Bridgestone that put useful information on the sidewall. Especially BFG that have paragraphs of info (just about!) with the most important for this application being: "Max load single 1380 Kg (3042 lbs) at 450 kPa (65 psi) cold". (Patrol 265 tyre) If I had these tyres on an F350 with a ton and a half in the tray, the tyres would be straight up to the 65 psi max as I know the manufacturer has tested it at these specs. The Patrol won’t be carrying anything like this so I’ll leave them where they are. 5. Tyre Life and Handling Vs Comfort – I like my comfort as much as the next person but I also like my machines to handle as well as they can. You’ll get a magic carpet ride if your boots are only carrying 22 psi but the extra rolling resistance is going to mean squeezing the accelerator that much closer to the floorboards and she’ll handle like the proverbial wet sponge. You wont be able to carry much speed through the corners with tyres wobbling around when they should be transmitting steering input to the road surface and all that flexing will be heating up the tyres. I’m not paying for the tyres but I don’t like wastage and the coil Patrols don’t ride too badly so I think 35 psi will be the lower limit that I run unless I’m on soft sand.

So … balance everything up and have a good look at the tyre placard and owners manual – it often lists alternative tyres that are fitted to different specifications of the model car that you drive and you can get a feel for what the manufacturer is trying to achieve. Be wary of the tyre and vehicle manufacturers' specs to a certain degree, as they are more likely to recommend low tyre pressures to give the impression that their stuff gives a lovely soft ride. They know that the average person is not going to push the tyre to anywhere near its limits and they are really not going to be broken hearted if you have to replace your tyres more often. Call me a cynic.

It really is one of those areas that a lot of people have no regard or understanding of, but if you were able to see how a decent pressure improves the handling, braking and general feel of your machine and makes it cheaper to run – you’d check them more often and keep them firm.

All this text applies to trailers as well and, in the case of box trailers, due to their lighter mass generally, they are one of the few areas where you may find over inflated tyres. The crude leaf spring suspension – never maintained – so the rusty leaves bind and this offloads a lot of the springing to the tyres in lightly loaded applications. If your tyres are rock hard you’ll shake the trailer to bits and everything on it. Conversely if you have a large boat that comes in around 2 tonne like mine does, or anything heavy for that matter, the tyres are often small to keep the load closer to the ground. This means they are working overtime and should be of the light truck (LT) variety and be pumped up to around 40 psi.

Now to muddy the waters a little…I’ve just read the Tyre Tips column in the Jan 2000 Overlander magazine by columnist Allan Finnie who was complaining bitterly about the fact that his new 4X4 was delivered with 36 psi in the tyres causing the ride to be ‘atrocious’. I would have been impressed myself but Allan did not state what sort of car he was talking about – only saying the tyre placard stated 26 front, 29 rear. He did say that the tyres were wide and low profile - and the car could have been a lightweight Honda CRV or something but he made no mention of handling or braking. He was right to say that lower pressures play a major part in how the car is perceived – especially on a trip around the block test drive – but its what he doesn’t say that worries me.

The modern 4X4s are getting more powerful, more comfortable with better brakes and handling. The driver these days needs good quality tyres and enough pressure in those tyres to transmit all this progress down to the road and give a bit of valuable feedback through the steering wheel and seat.

Enjoy your rubber

Jonesy


AnswerID: 6741

Reply By: Revs - Wednesday, Sep 18, 2002 at 00:00

Wednesday, Sep 18, 2002 at 00:00
4WD Tyres



What pressure do you put in these damn things?
Most of us probably ask ourselves this question as we try and fit the bent mangled service station doohickie that never seems to seal first try onto our tyre valve and press down the lever. It’s a good question and one I’ve never heard a definitive answer for. Of course there is no definitive answer for any category of tyre but I’ll do my best to shed some light on this shadowy subject.

First up, we have to grasp the concept that the amount of air we squirt into a tyre should be proportional to the size of that tyre and load applied to it. It is the internal air pressure that supports that load and allows the tyre to perform its intended function. Picture the tyre on your racing pushbike if you cut a section as long as your finger out of it. If you looked at it end on, its section thickness wouldn’t be much more than that of your thumb. If you could seal the ends and pump it up to 20 psi or 136.2 kPa you would find that you could crush the thing flat with your thumb and forefinger. Now go outside and cut the same section from your neighbour’s fat tyres on his Pajero (only kidding) and you’ll see it has the sectional thickness of a watermelon or thereabouts. Pump this up and try to crush it and you’ll need a hydraulic jack. This is a function of the physics of force and how it applies to cross-sectional areas. This is why your racing bike needs 70 psi and your car probably needs half that.

Now, if I haven’t confused you too much, how does this relate to your buckin’ and bouncin’ Hilux you may ask - as someone told you that 38 psi would do the job admirably. Well, it would on a heavier machine but assuming yours has been fitted with the almost standard after market fitment of 31 X 10.5 X 15 Desert Duelers or BFGs – its going to kick and jump around. The standard factory fitment for the Hilux utes was a 205R16 that was about an inch and a half shorter and 4 inches narrower. You have a much bigger tyre on a relatively light vehicle so the tyre pressures could easily come down to 26 – 28 psi. Now if you fitted the same rubber to an 80 series Toyota with its extra 600 kg mass and about triple the horsepower you’ve got a different situation altogether. The tyres would bulge and the car would ‘lurch’ on the corners as the sidewalls wobbled. If it were my machine another 10 pound would be added straight away maybe even 14 to make a 40 psi (272.4 kPa) total to get the machine to handle safely and enjoyably.

During my years of safety training we did a fair bit of driver training in sedans and 4WDs. The instructor we used a lot was a true gentleman by the name of John Van Leeuwen who runs Drivesafe Australia in WA and is an accomplished kart and Formula Ford state title holder. He loves his machines and understands the mechanics of them better than most. He made no secret of the fact that he likes people to err on the side of pumping their tyres up to the upper end of the manufacturers recommendations. After participating in many of the driving courses most of us got to dislike the heavy steering and sloppy handling of under inflated tyres and found it harder to modulate the brake pedal to achieve an emergency stop.

There is also the matter of tyre wear that increases with under inflation. To give you an idea of why tyres wear out with every day use – stand back and have a look at the round black things on the rims of your car and… you’ll notice that they’re not exactly round. Where they touch the road is flat and the sidewall bulges out noticeably at this point. If you were to let more air out of your tyre the flat section would get longer and the bulge bigger. As you are bowling down the road your tyre tread and sidewall are continuously bending and flexing and, where it meets the tar, rubbing against the road. This generates an enormous amount of heat which is the sworn enemy of tyre wear and degradation. If your heat a tyre up enough you could peel it apart with your hands. This flexing is the reason why manufacturers of tyres and cars recommend that you increase tyre pressures by 4 psi or 28 kPa when you are going on a trip to the country (or loading up your rig).

So what do we do about pumping up our tyres? I personally start with a median tyre pressure of 35 psi and work my way up or down from there depending on the situation that I’m faced with. If your interested – and most motor enthusiasts are – I’d follow a 5 step plan and add your own personal fuzzy logic factor just to make it more interesting. To add a personal touch, I’ll relate the logic to my work truck, which is a Patrol king cab GQ with 16 X 8 wheels and 265/75/16/ BF Goodrich Mud Terrains.

1. Tyre Size – Are they generally a large tyre in relation to what similar vehicles wear? Are they larger than what is on the tyre placard for that vehicle? Yes and yes – I might drop them to 33 psi.

2. Load – Is the vehicle loaded/heavy, likely to carry a load or tow a trailer in the near future? Nope, but it’s a 6 cylinder diesel and they are traditionally nose heavy – I might bump the fronts up to 35 again.

3. Speed – Are highway (freeway?) speeds likely? Are we in the middle of a warm season that will make the flexing heating problem worse? Yup yup – I’d better whack the drivers and steerers up to 38 all round.

4. Tyre Rating – You have to admire the quality tyres like BF Goodrich and Bridgestone that put useful information on the sidewall. Especially BFG that have paragraphs of info (just about!) with the most important for this application being: "Max load single 1380 Kg (3042 lbs) at 450 kPa (65 psi) cold". (Patrol 265 tyre) If I had these tyres on an F350 with a ton and a half in the tray, the tyres would be straight up to the 65 psi max as I know the manufacturer has tested it at these specs. The Patrol won’t be carrying anything like this so I’ll leave them where they are. 5. Tyre Life and Handling Vs Comfort – I like my comfort as much as the next person but I also like my machines to handle as well as they can. You’ll get a magic carpet ride if your boots are only carrying 22 psi but the extra rolling resistance is going to mean squeezing the accelerator that much closer to the floorboards and she’ll handle like the proverbial wet sponge. You wont be able to carry much speed through the corners with tyres wobbling around when they should be transmitting steering input to the road surface and all that flexing will be heating up the tyres. I’m not paying for the tyres but I don’t like wastage and the coil Patrols don’t ride too badly so I think 35 psi will be the lower limit that I run unless I’m on soft sand.

So … balance everything up and have a good look at the tyre placard and owners manual – it often lists alternative tyres that are fitted to different specifications of the model car that you drive and you can get a feel for what the manufacturer is trying to achieve. Be wary of the tyre and vehicle manufacturers' specs to a certain degree, as they are more likely to recommend low tyre pressures to give the impression that their stuff gives a lovely soft ride. They know that the average person is not going to push the tyre to anywhere near its limits and they are really not going to be broken hearted if you have to replace your tyres more often. Call me a cynic.

It really is one of those areas that a lot of people have no regard or understanding of, but if you were able to see how a decent pressure improves the handling, braking and general feel of your machine and makes it cheaper to run – you’d check them more often and keep them firm.

All this text applies to trailers as well and, in the case of box trailers, due to their lighter mass generally, they are one of the few areas where you may find over inflated tyres. The crude leaf spring suspension – never maintained – so the rusty leaves bind and this offloads a lot of the springing to the tyres in lightly loaded applications. If your tyres are rock hard you’ll shake the trailer to bits and everything on it. Conversely if you have a large boat that comes in around 2 tonne like mine does, or anything heavy for that matter, the tyres are often small to keep the load closer to the ground. This means they are working overtime and should be of the light truck (LT) variety and be pumped up to around 40 psi.

Now to muddy the waters a little…I’ve just read the Tyre Tips column in the Jan 2000 Overlander magazine by columnist Allan Finnie who was complaining bitterly about the fact that his new 4X4 was delivered with 36 psi in the tyres causing the ride to be ‘atrocious’. I would have been impressed myself but Allan did not state what sort of car he was talking about – only saying the tyre placard stated 26 front, 29 rear. He did say that the tyres were wide and low profile - and the car could have been a lightweight Honda CRV or something but he made no mention of handling or braking. He was right to say that lower pressures play a major part in how the car is perceived – especially on a trip around the block test drive – but its what he doesn’t say that worries me.

The modern 4X4s are getting more powerful, more comfortable with better brakes and handling. The driver these days needs good quality tyres and enough pressure in those tyres to transmit all this progress down to the road and give a bit of valuable feedback through the steering wheel and seat.

Enjoy your rubber

Jonesy


AnswerID: 6742

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