Tuesday, Dec 18, 2001 at 01:00
Jon, if in doubt, follow the manual. Given what you've said about the tyres riding only in the centre, they are definitely way over-inflated at 42psi. The guide I have read in a number of 4wd magazines is to run them for an hour at highway speeds, and then
check the pressures again. If the pressure has risen by 4psi they are inflated correctly, if less than 4psi they are over-inflated, if more than 4psi they are underinflated. The correct pressure is obviously very much related to load, when the vehicle is loaded for a trip away, the tyres will need to be harder than when you're just running around town unloaded. I have to admit I've never used this method myself, as I do so many different load trips in a short period of time. I just run at what's placarded on the vehicle, and boost the pressures in the rear tyres if I notice them bagging under a heavier load. I tend to run about 33psi all round, but I'm running a heavier vehicle on smaller tyres (750x16's). However, on long highway trips I have run them all at 50-60psi, so I get there a bit quicker, and on long dirt road trips, such as the
Gibb River Road in WA, I run at about 25psi, for better comfort and tyre life. On rough roads, a slightly softer tyre will not only be more comfortable, but will bend around rocks etc, and not puncture/fracture as easily.
I would start out with the pressure recommended in the manual, and work it out from there. the only advantage to harder tyres is a small reduction in fuel consumption due to a lower rolling resistance, but the ride is harder, and tyre wear becomes a lot more uneven. It's generally not worth it. Underinflated tyres also wear unevenly, and may be more prone to blowouts or rolling off the bead.
I realise that this rambles a bit, but in conclusion, lets face it, the tyre
shop wants to sell you more tyres, so if they wear out fast through the wrong inflation pressures, they'll get your business again sooner (OK, I'm a cynic). I hope this helps resolve your dilemma. Cheers, Alex.
AnswerID:
1622