Thread: Tyre pressures (again!)

I think it depends on what tyres are involved. Tyre places are used to working with highway tyres and some ATs.
The placard on my Disco says 4 psi more in the rear than in the front. However, that would have been with standard highway tyres 18 years ago, so the pressures are different with my current tyres.
I currently run 32 in the MTRs, but pump the rear up to 36 when towing. No real theory, it just seems to work.
Every time I get the tyres balanced the workshop pumps them up to 40, which is just too hard, so I have to let them down.

Hi

In reality the only sure way to tell is by the tread wear pattern, but by then your tyres are half gone !

I think I will try the 4psi rule and see where my pressures finish up.

These guys put almost 10psi over the compliance plate specs in the corolla

Steve

It's a strange theory, I have heard of it but never went with it.

The place I bought my tyres from who's past time was rally driving and extreme off-roading has mentioned to me that it is a comfort thing. Basically you don't want to exceed more than 5psi either way of the vehicles placard remembering that the pressure increases by about 4psi when it warms up. I.e in The P38s case 28psi in the front will run at 32psi at normal running temp, which makes sense condsidering such a low cold pressure rating in the first place. ATs & Mud terrains have harder sidewalls, so naturally it's ride is going to be harder, and they don't mind running a little lower in pressure like around 26psi (cold) in the front remembering the 4psi increase when warm.

It can be complicated, but highway tyres should run as close to placard as possible and higher if using lower profile like the 18' RR rims.

In the US there have been a large number of individual lawsuits towards tyre companies vs the tyre store vs the car manufactures due to their inconsistent guides on tyre pressures resulting in serious accidents if not fatalities for the wrong advise.

Many automotive Experts do agree that the manufactures placard is what we should be focusing on as that is what the vehicle has been tested on and signed off as.

Hi

I am inclined to stick with the compliance plate, rather than take the advice of some guy from a tyre store !

They put 38PSI all round in the corolla, which is basically a rollerskate on wheels, and suggest I put 40 or 42 all round in the P38.

I suspect Land Rover and Toyota have done a lot more testing than anyone else regarding tyre pressures for their cars.

As far as the 4PSI rule, as Andy pointed out, that's the kind of pressure increase you would expect to see anyway.

The physicist in me says a higher pressure means a slightly larger volume of air than a lower pressure but that is unlikely to lead to a big variation in pressures.

Steve

Steve

At one level I agree with the compliance plate. However, during advanced driver training courses I have attended they always suggest somewhat higher tyre pressures than the compliance plates (around 36 psi on a sedan) to improve emergency braking and improve steering responsiveness.
Then the other part of the equasion....load carrying. Going back many many years ago, I recall being advised that to achieve the correct pressure for the load being carried you first need a reference point of an unladened vehicle. With the car unladened and with the correct tyre pressure take a measurement in inches (yes it was that long ago) or mm of the ground to the centre of the wheel. When you load up the car the extra weight will give the apperance of having a flat tyre, simply pump up the tyre to achieve the height of the unladened vehicle (not pressure) and you will have the correct pressure for the load in the car.

Gary

Originally Posted by mtb_gary

Steve

At one level I agree with the compliance plate. However, during advanced driver training courses I have attended they always suggest somewhat higher tyre pressures than the compliance plates (around 36 psi on a sedan) to improve emergency braking and improve steering responsiveness.
Then the other part of the equasion....load carrying. Going back many many years ago, I recall being advised that to achieve the correct pressure for the load being carried you first need a reference point of an unladened vehicle. With the car unladened and with the correct tyre pressure take a measurement in inches (yes it was that long ago) or mm of the ground to the centre of the wheel. When you load up the car the extra weight will give the apperance of having a flat tyre, simply pump up the tyre to achieve the height of the unladened vehicle (not pressure) and you will have the correct pressure for the load in the car.

Gary

Yes that's true in theory, but over-inflating the load tyre can cause other issues such as an increase risk of a blowout with the load on the back, and that can't be good. If you're going down that path then again as long as you don't go above the tyre rating pressure then you should be ok.

Advance Driving courses may suggest that, and that's fine on racetracks in controlled environments with good Tarmac surfaces but unfortunately Australian roads especially in the country & outback areas are very ordinary. Like what happens if you suddenly end up on gravel road with tyres well above their vehicle's recommendation? It would be like driving on skates with every pot hole bouncing the wheels rather than absorbing the unevenness. I know these courses mean well, but in reality it can be a different case.

I'll chuck my 2c in!

I've run 3psi higher in the rear than the placard in my P38 for the entire life of the BFG's it's currently wearing, and 7psi higher in the front. Have done 40,000km so far and they are wearing perfectly across the tread. I expect they'll go another 40,000km as well.

See attached pic taken yesterday. Might not show the entire tread, but that's what 40,000km on muddies looks like.


Cheers
Keithy

Originally Posted by Keithy P38

I'll chuck my 2c in!

I've run 3psi higher in the rear than the placard in my P38 for the entire life of the BFG's it's currently wearing, and 7psi higher in the front. Have done 40,000km so far and they are wearing perfectly across the tread. I expect they'll go another 40,000km as well.

See attached pic taken yesterday. Might not show the entire tread, but that's what 40,000km on muddies looks like.


Cheers
Keithy

Keith, nothing to do with this thread but how stretched is the height sensor? From that pic it looks almost vertical?

Gary