Thread: D2 tyre pressures

Haven't read through the complete thread,but you guys are complicating it all.

The D2s i had,it was 18psi for sand(sometimes 20 if it was not to soft),36 around town & lightly loaded trips,38 to 40 loaded trips,particularly hot weather,32 corrugations such as Development rd on Cape.

These pressures were all round & mostly BFG A/T.

Around 85 to 90k out of a set so pressures were probably not to far away.

On a run,particularly in hot weather i would check tyre temperatures at stops.

I cannot understand how you guys drive with significantly higher tyre pressures in the rear than the fronts.....you must suffer some horrible understeer or you have no idea what understeer is......and therefore disregard or try to compensate for it. front plough understeer ugggghhhhh!

A quick recap: running tyre pressure is related to axle loading and the tyres maximum load and maximum pressure. The tyre pressure is adjusted according to loading to maintain the same springing rate and deflection in the tyre side wall front and rear.

The placard pressures are a compromise set on the basis that the d2 is loaded with 5 passengers and luggage. The front axle loading doesn't vary significantly as most of the additional load is carried over the rear axle.

With just the driver and no additional load there is little difference between front and rear axle loadings so you could reasonably run the same pressures. Once you start adding load - bullbar, winch, dual batteries, etc, the placard pressures are no longer applicable and should be adjusted to keep the same sidewall deflection//springing rate in all tyres.

Bottom line is that you should adjust the pressures on the basis of loading. Whether you do that by the +4psi rule, measuring footprint length or by weighing axle loads on a weigh bridge and calculating from there it doesn't really matter: the end result is pretty much the same.

cheers
Paul

Originally Posted by ramblingboy42

I cannot understand how you guys drive with significantly higher tyre pressures in the rear than the fronts.....you must suffer some horrible understeer or you have no idea what understeer is......and therefore disregard or try to compensate for it. front plough understeer ugggghhhhh!

Do you actually have a D2?

I don't believe the lower front tyre pressure is due to axle loading only. Many 4wds have similar loading to D2 but specify same tyre pressure back and front. I think it is due to the suspension setup as well.

I tried running 36psi in front and rear and at speed the front end was twitchy with no feel and gave me no confidence that it would go round the corners. I dropped the fronts to 32psi and it made a huge difference.
Landrover have not set these pressures just for the fun if it.

Offroad everything goes to 20psi.

I understand thats exactly why LR have low front tyre pressures - to take the twitch out of it.

Originally Posted by walker

Do you actually have a D2?

I don't believe the lower front tyre pressure is due to axle loading only. Many 4wds have similar loading to D2 but specify same tyre pressure back and front. I think it is due to the suspension setup as well.

I tried running 36psi in front and rear and at speed the front end was twitchy with no feel and gave me no confidence that it would go round the corners. I dropped the fronts to 32psi and it made a huge difference.
Landrover have not set these pressures just for the fun if it.

Offroad everything goes to 20psi.

I also had the same experience and strangely enough also tested 36psi and went down to 32psi. I have an ARB winch bar on the front. I found that the 28psi was too soft for my liking. My rears are normally 35-36 psi empty around town and 40psi loaded on country runs.

Cheers
Ron

I've finally managed to find the document that the calculations are based on which I've attached for those who are interested.

"Inflation Pressures at Less Than Maximum Tire Loads"
written by John W. Daws, Ph.D., P.E. Daws Engineering, LLC.
The paper was presented at the September 2009 Meeting of the Tire Society

There is a obviously a bit of math but the text is contains a good explanation and discussion so it's easy enough to get your head around.

The equation I've used above is basically equation [9]:

Code:

(pressure /max pressure) = (load/max load)

which the conclusion states:

5. The simple ratio method given by Equation 9 provides a slightly more conservative, but computationally simpler, method of developing a safe operating pressure for tires operating at less than maximum loads.

Equation 9 can be rewritten as:

Code:

pressure = (load/max load) x max. pressure

You need to account for the fact that the rear axle load is split across two tyres so a 925Kg maximum loading per tyre gives you a maximum axle loading of 1850kg.

With a full rear axle load of 1720kg and 925Kg load rating tyres which have a 50psi max inflation (as per the stock michelins):

pressure = (1720/1850) x 50
pressure = 0.929729 x 50
pressure = 46.4psi

The placard pressure is 46psi for this loading.

cheers
Paul

Originally Posted by ramblingboy42

I cannot understand how you guys drive with significantly higher tyre pressures in the rear than the fronts.....you must suffer some horrible understeer or you have no idea what understeer is......and therefore disregard or try to compensate for it. front plough understeer ugggghhhhh!

No my D2 was perfect with 32 front and 40 rear, now read Offtracks post below and the document he has posted above, doesn't get any clearer than that.

Originally Posted by OffTrack

A quick recap: running tyre pressure is related to axle loading and the tyres maximum load and maximum pressure. The tyre pressure is adjusted according to loading to maintain the same springing rate and deflection in the tyre side wall front and rear.

The placard pressures are a compromise set on the basis that the d2 is loaded with 5 passengers and luggage. The front axle loading doesn't vary significantly as most of the additional load is carried over the rear axle.

With just the driver and no additional load there is little difference between front and rear axle loadings so you could reasonably run the same pressures. Once you start adding load - bullbar, winch, dual batteries, etc, the placard pressures are no longer applicable and should be adjusted to keep the same sidewall deflection//springing rate in all tyres.

Bottom line is that you should adjust the pressures on the basis of loading. Whether you do that by the +4psi rule, measuring footprint length or by weighing axle loads on a weigh bridge and calculating from there it doesn't really matter: the end result is pretty much the same.

cheers
Paul

Excactly

Originally Posted by walker

Do you actually have a D2?

I don't believe the lower front tyre pressure is due to axle loading only. Many 4wds have similar loading to D2 but specify same tyre pressure back and front. I think it is due to the suspension setup as well.

I tried running 36psi in front and rear and at speed the front end was twitchy with no feel and gave me no confidence that it would go round the corners. I dropped the fronts to 32psi and it made a huge difference.
Landrover have not set these pressures just for the fun if it.

Offroad everything goes to 20psi.

Yep the higher pressure in the front makes for a very twitchy car.

Originally Posted by Slunnie

I understand thats exactly why LR have low front tyre pressures - to take the twitch out of it.

Yep, what he said!!

Baz.