tyre preasure

gday. im new to the 4wd thing and i was wandering what tyre preasures to use on coregated roads. I know that 20 psi works great on the sand and rocks ,but i am wandering how low you can go before you start having problems with tyres breaking beads etc. Ive heard alot of different things but would like to hear from people who have tested it. I will be towing a van and would need to know if tyres work in the same way on the trailers etc
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Reply By: River Swaggie - Friday, May 04, 2012 at 19:57

Friday, May 04, 2012 at 19:57
Hiya Trev

depends on the tyre but in sand down to about 10psi some may say 8psi...It also depends on the way you drive too...Take it slowly,dont spin the wheels the tyres will come off then...

If your stuck take out a few psi at a time,there's no hurry generally lol...

Heres a rough idea...





Goodluck
AnswerID: 484974

Follow Up By: Trev&Ness B - Friday, May 04, 2012 at 20:07

Friday, May 04, 2012 at 20:07
cheers for that

would it be worth runing tubes in the tyres. the only thing i think could be a problem is ripping the valve stem off when you give it some stik. Would you run the tyres that low on coregations?
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Follow Up By: River Swaggie - Friday, May 04, 2012 at 20:36

Friday, May 04, 2012 at 20:36
Hiya Trev

I wouldn't and refuse too...My main area of travel is Dargo,Licola,Butcher Country,Walhalla,Woods Point etc etc...

Get yourself a ARB Tyre repair kit...There about 60 bucks from memory....Also because of the rocky/shaley areas i go the tyre has become unseated in heavy rocky ledge areas,so it lets out about 2 psi over a day or possibly a bit more,just take the Tyre down to be reseated...A couple of times there been quick in suggesting the inner tube route...until i tell them what i want,knowing it wasn't a puncture....

"Would you run the tyres that low on coregations? "

Depending on your load mate..20-25 psi should be ok for an average dirt road depending on the severity of the coregations...

The beauty is you can trial it yourself out there.....

Oh another thing is Google the 4 psi rule.....It may suit you....i don't use it myself and never had a puncture.But i do run 31's MT MTZ's......

They have been great...

Goodluck

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Reply By: Member - nick b - Friday, May 04, 2012 at 20:25

Friday, May 04, 2012 at 20:25
Trev&Ness ..Try a search on this - google & exploroz - ,has been on the forum not that long ago .
Cheers Nick b
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Reply By: Allan B (Member, SunCoast) - Friday, May 04, 2012 at 22:20

Friday, May 04, 2012 at 22:20
Depends on vehicle weight, tyre type etc but try taking them down to 25 psi and a maximum speed of 80km/h for a start and make a judgment. All tyres same pressure, van included. Check on tyre temperature after 15 minutes, raise pressure or lower speed if getting too hot.

You will not have bead seal problems down to 15 psi or lower unless you are traversing tracks with large rocks or deep ruts that exert lateral forces on the tyre.

Cheers
Allan

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Reply By: rainbowprof - Saturday, May 05, 2012 at 00:02

Saturday, May 05, 2012 at 00:02
so on a troopy running 75 psi on 16" split rims (16 ply conventionals) fully loaded with trailer one could drop the pressure to 25 psi on corrugated roads like the Tanami or Urandangi road (Plenty Hwy)? Is that the consensus? Then one wouldn't sit on 80 kms an hour, I presume. Same vehicle 15 psi in the sand?
AnswerID: 484992

Follow Up By: Life Member - Phil B (WA) - Saturday, May 05, 2012 at 02:15

Saturday, May 05, 2012 at 02:15
Hi rainbowprof

People "running 75 psi on 16" split rims (16 ply conventionals) fully loaded with trailer " are the reason the corrugations got here in the first place.

cheers
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Follow Up By: Off-track - Saturday, May 05, 2012 at 13:27

Saturday, May 05, 2012 at 13:27
BS
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Follow Up By: rainbowprof - Saturday, May 05, 2012 at 14:51

Saturday, May 05, 2012 at 14:51
Phil, I doubt that I am personally responsible for the corrugations. Driving a vehicle with 6 occupants, food, camping equipment, etc. adds up in weight and I run the tyres in accordance with the recommended preesures labelled on the tyres- I was running it 15 lbs below the maximum- the maximum pressure being related to the load bearing capacity of the tyres. My suspension is such that it is not a very rough ride inside the vehicle. I believe every vehicle contributes in some way. Vehicles with one or 2 passengers, less weight and lower tyre pressure are no less to blame as it would then take 3 to six times as many vehicles to transport said 6 people:-) Interestingly, and I quote:

Lloyd Junor, who has spent many years travelling the Outback, agreed (with the theory of wind and 'dirt dunes'). He also pointed out that, "Corrugated roads have the corrugations road-wide, not precisely where the vehicles' wheels traffic them. So traffic does not explain the corrugations.

Another theory on an oft debated topic. These tyre pressures may have contributed to the fact that I had no fllats/ punctures on a 15 000 km trip.
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Follow Up By: Allan B (Member, SunCoast) - Saturday, May 05, 2012 at 16:01

Saturday, May 05, 2012 at 16:01
Yes Rainbowprof, I drive a Troopy, 3600kg loaded. I run the Cooper S/T's at 40/45 on the bitumen, 30/35 or 25/30 on unsealed, and 18/18 or 15/15 on soft sand. My vehicle is fitted with tyre pressure monitors so I am able to supervise the pressures and temperatures and the above cold pressures remain within +15% tolerance during driving. In my case the lower pressure on unsealed really does make a difference with corrugations. However I have noticed a reluctance of some drivers to lower tyre pressures due to apprehension perhaps caused by years of hearing expressions about maintaing "correct" pressures, aimed of course at city drivers and bitumen speeds.

I researched the corrugation thing a while back and it seems that while there are a lot of unsupported theories, there has not been an accepted detailed scientific explanation for their creation. As you say, the corrugations are road-wide, although it could be argued that is caused by vehicles moving to the side to evade existing corrugations. On the other hand I have never seen corrugations on a track that has only experienced a very few vehicles and at low speeds such as a private station track. So I would believe that vehicle volume and speed seems to be a cause but the issue of higher tyre pressures being the culprit is an unsupported perception only.

However the blame for scolloping on the approach faces of sand dunes can be clearly placed on excess tyre pressure simply by observing the wheel-spin of vehicleswith high tyre pressures, aided and abetted by an overabundance of power. My 3600kg naturally-aspirated Troopy regularly climbs dunes at 18psi without breakneck run-up or kangarooing wheel-spin.

Cheers
Allan

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Reply By: olcoolone - Saturday, May 05, 2012 at 11:08

Saturday, May 05, 2012 at 11:08
This will be interesting!
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Follow Up By: Member - Old Girl - Saturday, May 05, 2012 at 14:28

Saturday, May 05, 2012 at 14:28
Your not wrong.
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Reply By: rainbowprof - Saturday, May 05, 2012 at 14:53

Saturday, May 05, 2012 at 14:53
and I hope it is. I would love some constructive feedback.
AnswerID: 485045

Follow Up By: Rockape - Saturday, May 05, 2012 at 16:27

Saturday, May 05, 2012 at 16:27
rainbowprof,

There is no hard evidence as to how they are formed but here are a few things for all to think about.

Corrugations only occur in certain types of soil.

Corrugations are much worse where vehicles come over a rise and find they have to either apply the foot brake or engine brake to slow for a gully or one lane bridge.

Corrugations are worse on a bend and that is either partly to blame on water run of due to the camber. Most of it is caused by vehicles.

I know that when the track is real bad towing a 988 tyre behind a semi or road train certainly takes the sting out of them.

Re tyre pressure, I know I can run at 30 to 40 kph on hard rocks at 10 psi and never have a problem. Often we don't have any replacement tyres so we just keep pumping them up day after day.

I know you probably love your split rims but I have the opposite reaction to them.

All the best,
RA.
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Reply By: rainbowprof - Saturday, May 05, 2012 at 17:31

Saturday, May 05, 2012 at 17:31
Thaks muchly for your input, gentlemen. There does seem to be a lot of variation between tyre pressures depending on the vehicle configurations, terrain and personal preferences. It is certainly an absolute that reducing tyre pressures in sand is necessary. I thought on hard terrain with high pressure the pressure in the tyres helped sidewall strength. To quote: "Correct air pressure in your tyres is as important as giving your engine a tune up. The economic benefits are perhaps even greater! With the right amount of air pressure, your tyres wear longer, save fuel, enhance handling and prevent accidents. The effects of not maintaining correct air pressure are poor fuel mileage, loss of tyre life, bad handling (perhaps even loss of control), and potential vehicle overloading."

Note how the air pressure increases with plus sizing to meet the load carrying capacity for the car. Perhaps the most overlooked factor is vehicle loading for trucks and 4WDs. Since these vehicles can be configured and loaded in many ways, the proper inflation pressure should be determined by actual tyre loads and respective tyre types. . Running 7.50 x 16 , high profile by definition, may require more air than radials which tend to have a lower profile (x/70 or x/80). I have run 40 or 50 psi with the 15" radials. The current tyres and pressures have contributed to long distance fuel economy and a rigid, safe feeling with driving control. And the high profile and high pressure have given over an inch lift. They sag a good half an inch at 50 psi.

I notice another member (Hughesy from SA) said:

Some 14ply Michelins I had could be run at 100psi and the current Bridgestones I have just put on are 10ply and have a max pressure of 80psi.


AnswerID: 485057

Reply By: gbc - Sunday, May 13, 2012 at 20:09

Sunday, May 13, 2012 at 20:09
Adam's sign at the Pink roadhouse has loaded troopys with tubes on splits running 30 psi front and 36 psi rear as an optimum pressure for that stuff. This is 10 psi higher than equivalent rating for a large loaded 4wd on 16's.
He also says splits and tubes are the single WORST performing tyre combination going round.
Take it, leave it, mull it over, but the bloke has seen a few different tyre combos in his time.
Personally I don't think he's too far wrong.
AnswerID: 485731

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