Thursday, Feb 23, 2006 at 20:45
G'day Luca. It never ceases to amaze me how freely folk with the best intensions give out bad advise on here.
In answer to your querie, EVERY vehicle is different! If you have the same model vehicle, same tyres, same springs, same shocks, same accessories, similar driving style then they will all run the same pressures, otherwise they WILL be different.
I have Cooper S/T's (265/75R16LT) on my bog stock GUIII Patrol, 3 litre manual with 50mm raised HD King Springs in the front and EHD Kings in the back, all controlled by Koni Heavy Track shocks adjusted up 1/2 turn on the front and one full turn from there softest setting on the rear. I rotate the 4 of them every 5,000k's and after 13,000k's of fast bitumen and dirt road driving they have worn 1.7mm, and I like having my fun through the corners.
I run 39psi front and 37psi rear and nearly everyone I have spoken too tells me that is way to high, but I believe the wear figure and handling speaks for itself.
To work tyre pressure out for yourself, here how I did it.
1. Have your vehicle weighed on a weighbridge in it's normal "everyday use" form, include a full tank(s) of fuel, all the gear you normally carry and a passenger or 2 if thats what's normally in there. First, weigh the front axle, then weigh the rear axle.
2. Look on the side of the tyre and Cooper supply a maximum rated load at a maximum pressure. NEVER exceed this maximum pressure figure. My Coopers have a maximum pressure of 80psi (550kpa), at rated load of 1550kg's, the previous Bridgestones (265/70R16 Duellers, D693's I think) had a MAXIMUM pressure of 36psi at their rated maximum load, big difference! If your tires don't have this
information, a quick email to the Australioan distributor will fix this.
3. Now, start with the front axle weight figure and divide it by 2,
mine are in brackets (F - 1320 kilo's divided by 2 = 660kilo's per tyre). Now divide the maximum tyre pressure by the rated maximum load number (80psi divided by 1550kg = 0.0516) Now multiply the answer by the amount of weight on each front tyre (0.0516 X 660 kilograms = 34.06), so the starting point was 34 psi for me.
4. Now repeat the same calculations for the rear.
I kept monitoring heat build up over the next week until I arrived at my 39psi cold F and 37psi cold rear, which give me a nice 3-5psi heat build up after an hours highway running.
The upside of all this troublesome work is a vehicle that handles exceptionally
well, especially in the wet, brakes in a straight line, steers where you point it, has a firm but not harsh ride and excellent, even tyre wear IMHO. The original Bridgestones were buggered on the rear at 26,000k's, never rotated I'm guessing.
Sorry about being long winded, I hope this answers all your questions.
Cheers,
Peter
AnswerID:
156746
Follow Up By: Member - Dedalus (SA) - Thursday, Feb 23, 2006 at 21:37
Thursday, Feb 23, 2006 at 21:37
Thanks! I think my total weight is 3.6 tonns .... At the moment I'm driving with 34 psi in front and 36 psi on the back... very good confort here in
Kangaroo Island but I think not enought for Hiway driving .... maybe 36-38 fronf + 38-40 rear???
Thanks!
Luca
p.s. I have 50 mm lift kit from OEM (springs + shockers) , cargo barrier, a full rook rack (4 legs) , alluminium bull bar + me, my whife and my 5 monts old daughter ....
FollowupID:
410856
Follow Up By: P.G. (Tas) - Friday, Feb 24, 2006 at 11:59
Friday, Feb 24, 2006 at 11:59
G'day again Luca. The figures you suggest are at best a guesstimate, and you MAY get away with them, but I believe it is better to be sure than sorry.
I have done some homework for you. I'm assuming the tires are 10 ply 265/75R16LT Cooper ATR's. They have a listed load carrying capacity of 1550kg per tire and the assumption is also they have a maximum rated pressure of 80psi@20 degrees C (same as the S/T's) .
I don't know about your weight distribution between front and rear, so I will guesstimate about 60% rear and 40% on the front. Working on as gross weight of 3.5 tonnes, I came up with these figures.
Front 36 psi + 2psi for heat build up + 2psi for high speed highway driving = 40psi as a starting point.
Rear 54 psi + 2 psi for heat build up + 2psi for high speed highway driving = 58psi as a starting point.
The rest is up to you to work out. I strongly recommend no more than 6psi heat build up after 1 hour of normal highway driving, if you are after comfort, but preferably aim for the 3-5psi heat build up if you want to get the best out of your vehicle and tyres.
Remember, if you get more than 3-6psi build up the tires need more air, and if you get less, lower the pressures, and always
check them before you move off in the morning. A kilometre of driving to the local servo will throw the whole process out of wack.
Heat is a tires worst enemy. It is the major cause for blowouts, tread separation and fast tread wear. Many tires have been branded duds or hopeless for the want of a bit of air.
Hope this helps.
Cheers,
Peter
FollowupID:
410987