Tyre pressures (again!)

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Originally Posted by SteveFarmer

Hi

I recently had a conversation with a guy in a tyre place who stated that "tyre construction has been revolutionised over the last 5 years and you should run higher pressures than the compliance plate recommends"

I mentioned the the P38 recommendations are 10PSI less in the rear, and his response was "You should run at least 40PSI and I run 42PSI all round in my car"

I have been doing a little research and this 4si rule seems to be pretty well researched, though I have never heard of it before

4psi Rule

Anyone used this rule?

Steve

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I reckon stick with the 4psi rule. I've been using it for a number of years now and I think it's great. I'm on placard in the rear of my D2 and 4psi over at the front (due to bulbar etc) and it's 4psi up when hot at both ends. Perfect :D:D

And tyres have not been revolutionised in the last 5 years IMHO. I would argue that hey have changed compounds and added stuff like silica etc but they are still round and black and haven't changed dramatically in the last 20.

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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.
https://www.aulro.com/afvb/

Cheers
Keithy

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Again, it's a comfort thing. If riding on higher pressure is your driving pleasure then you go with the flow.

I actually put 30psi (cold) in the front and standard 38psi (cold) in the rears and find a balanced mix of lesser roll resistance without compromising the ride comfort. Don't forget that it's not just the tyres that get affected but your shocks too, as they're made to work harder to absorb the extra vibration.

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Originally Posted by gusthedog

And tyres have not been revolutionised in the last 5 years IMHO. I would argue that hey have changed compounds and added stuff like silica etc but they are still round and black and haven't changed dramatically in the last 20.

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I agree. If anything tyre technology is still behind the times.

I.e not catering Mud terrain for lower profile rims for RR sport, Discovery 4, L405 RR. In fact I reckon off-road tyre companies are still a good 10 years behind the times, thinking that we all still drive MQ Nissan Patrols, 80 series Lancruisers etc. when just about all new 4wd's are now going lower in profile and there are very limited choices out there.

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Originally Posted by redandy3575

I agree. If anything tyre technology is still behind the times.

I.e not catering Mud terrain for lower profile rims for RR sport, Discovery 4, L405 RR. In fact I reckon off-road tyre companies are still a good 10 years behind the times, thinking that we all still drive MQ Nissan Patrols, 80 series Lancruisers etc. when just about all new 4wd's are now going lower in profile and there are very limited choices out there.

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The problem with modern vehicles is the speed rating.

What sort of mud tyre gets a 200km/h speed rating?

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Originally Posted by Dougal

The problem with modern vehicles is the speed rating.

What sort of mud tyre gets a 200km/h speed rating?

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Not many, but then again Muddies aren't meant for speed, they're for off-road use usually with a 140kmh max rating.

Certainly ups the challenge for tyre companies eh!!

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Originally Posted by redandy3575

Not many, but then again Muddies aren't meant for speed, they're for off-road use usually with a 140kmh max rating.

Certainly ups the challenge for tyre companies eh!!

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Especially in countries where the speed limit is 130km/h or more.

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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

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So 65psi to achieve this was right! Hayman Reece probably didn't like the ball load, and the suspension didn't drop an inch. :D

The placard was signed of with Michelin xpc too. With my current road tires anything less than 32 cold and they loose grip, so I run 36 front and rear, though 40 in the rear when loaded up.
I used to run 36 and 40 cold with the bfg at's. Only because with the LT carcass I didn't want it flexing to much and building up heat.

These pressures are just what feels good.

So he's saying that tires now are more flexible in the side wall?

I run 39psi in the back and 36psi in the front cold, when warmed up they only ever move around 2psi according to my tpms . This is pretty close to what the installer recommended to me as he pushed a coopers tyre manual/tips and tricks booklet in my hand with all that 4psi stuff in it...

All good so far:D:D

Rob

The increased rolling resistance is certainly noticeable with the Dueller 697s I now have instead of the previous Cooper H/Ts. So is the increased fuel consumption!!
Increasing the fronts up from 28 to 34psi improves the "rolling g" sensation, while the bumps and cracks in the bitumen are largely absorbed by the still new thick tread.

I had understood that the tyre pressure differential was also something to do with putting a slight preload on the viscous coupling in the transfer box due to the slightly increased diameter of the rear tyres due to their pressure. Perhaps this is a bit of a myth?

The blokes at the local Goodyear where I got the Coopers years ago were adamant that 35 psi front and rear was Cooper recommendation... damned if I know!

Edit: another thought regarding the VC. If there is a difference in overall diameter between front and rear tyres at the recommended inflation pressures, sufficient to preload the VC then am wondering if this may result in a degree of trasmission windup causing otherwise unexplained vibration at higher speeds? I have some experimenting to do!

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Originally Posted by Keithy P38

http://www.aulro.com/afvb/attachment...-rover-070.jpg

Cheers
Keithy

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Nice home made extended bumpstop! :D What do you do when the cable tie breaks ?:eek: