Tyre Pressures

Submitted: Monday, Mar 31, 2003 at 08:50
ThreadID: 4138 Views:2552 Replies:5 FollowUps:4
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I havew read here and on other forums about setting tyre pressures by the 4psi rule. My question is if after your long drive to get the tyres hot your pressure as increased less than 4 psi do you need to put more air in when cold or less?. We have so little time to enjoy our land
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Reply By: ThePublican - Monday, Mar 31, 2003 at 09:30

Monday, Mar 31, 2003 at 09:30
Less than 4psi = to high initial pressure.
Over 4psi = to low initial pressure. .... Reason being to low a pressure=more flex=more friction=more heat=increase in pressure.
AnswerID: 16470

Reply By: Rob from Cairns Offroad Training & Tours - Monday, Mar 31, 2003 at 09:36

Monday, Mar 31, 2003 at 09:36
If the pressure has increased by less than 4 lb the pressure was too high to start with. As a matter of interest What size are your tyres, brand and what pressure are you running? I always train people in their own car and I am constantly surprised at the high tire pressures people tend to run in the mistaken belief more pressure means less punctures. The correct pressure allows the tire to conform to the terrain and also become a factor in suspension resulting in a more compliant ride.
Cheers RobCairns Offroad Training & Tours
AnswerID: 16471

Follow Up By: Truckster - Monday, Mar 31, 2003 at 10:30

Monday, Mar 31, 2003 at 10:30
I agree with people running too high pressures..

Theres one bloke on another forum runnin 65psi in his, i cant imagine how rough the ride would be.
FollowupID: 10146

Follow Up By: Member - David now Outnabout - Monday, Mar 31, 2003 at 13:17

Monday, Mar 31, 2003 at 13:17
The tyres are 265/75/16 Goodyear Wrangler AT/S and have a load rating of "D" and fitted to a Parado TD. I have had Prado's since 1996 and have always had the standard road tyres or AT tyres but not light Truck. In all the tyres I founs 34psi to be ideal. When I had the Light Truck tyres fitted I was told 38 PSI which gives a very harsh ride and I noticed the rubber "pips" wer not wearing off on the outside indicating overinflation. A mate of mine has an 80# and runs 32 psi and has pertfect wear. So I have been experimenting with air pressure by dropping to 34, 32, and now 30psi when cold. The ride is a lot better now but the pressure is only going up 2psi. Do I dropp them another 2psi down to 28 which is the recommended pressure for standard Grand treks even though when running them I found it best to have them at 34psi other wise they wore on the edges.We have so little time to enjoy our land
FollowupID: 10156

Reply By: David - Monday, Mar 31, 2003 at 13:04

Monday, Mar 31, 2003 at 13:04
Some people may be running pressures too high..... but there are far more are running too low, atleast as far as family hacks for the bitumen. Yes they need to be lowered for off road, but when back on the bitumen they should go up again. Running proper pressures (at the UPPER limit of recommended book pressures) will give better handling, stopping and tyre life, with even more difference noticeable in the wet, as dynamic aquaplaning speed is directly correlated to tyre pressure (higher tyre pressure gives higher aquaplaning speed).
When r,unning lower pressures, all of the above will suffer badly- only benefit will be a slightly smoother ride.
Moral of the story is check your pressures more often, and run them on the high side of recommended. By all means lower them off road- but beg steal or borrow a compressor and pump them back up ASAP when you back on the tar.... I'll bet anybody a carton or two there are more people driving around with pressures too low rather than too high (and ALL the motoring associations eg NRMA etc agree with me )
AnswerID: 16495

Reply By: Michael- Monday, Mar 31, 2003 at 22:04

Monday, Mar 31, 2003 at 22:04
Interested in all this tyre pressure business. Has anyone any knowledge of the term 'Static Load Radius'? The SLR is a figure published by the tyre manufacturer for all their model tyres. It is a constant figure no matter what the load. That is the tyre radius is measured with any given load and the pressure adjusted to match the given figure for your tyre. Adjustments have to be made for tyre wear and road surface but it does give a good starting point that I have found very useful.
AnswerID: 16536

Follow Up By: Member - Mike - Tuesday, Apr 01, 2003 at 08:39

Tuesday, Apr 01, 2003 at 08:39
Mike, I am interested in this SLR. Where do I find it or information about it. Advice please.
MikeToo little time in the bush!
FollowupID: 10205

Follow Up By: Member - David now Outnabout - Wednesday, Apr 02, 2003 at 15:12

Wednesday, Apr 02, 2003 at 15:12
Michael you have got me interested in this two and it sounds logical. Since my original posting I have been to several different Beaurepaires sites and got conflicting views on pressures. The damn things will run up to a maximum of 65 PSI but how do I know how much to put in them. Do I put 5 or 25 extra psi in them. So you see that what you suggest may be the way to go. Know one at the Beaurepaires shops has heard abou the SLR so I have now emailed their technical department. If you have any further info please post as I am sure there are many who would be interested in it.We have so little time to enjoy our land
FollowupID: 10323

Reply By: Michael - Wednesday, Apr 02, 2003 at 22:13

Wednesday, Apr 02, 2003 at 22:13
The static load radius measurement is available but often only from the technical departments. I have Hankook tyres and they do publish a good detailed guide to their tyres. It does not however give the SLR measurements. I obtained the measurement from the tyre store. They had a more sophisticated guide. It is a measurement worthwhile following up and I should think that the technical department of any tyre manufacturer should be able to let you know the value for any of their products. It does not surprise me that the tyre sellers don't know of this measurement. It is however available. Good luck
AnswerID: 16742

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