tyre pressure

I run the recommended pressures in my P38A and did the same in my previous RRs (classics), i.e., 28 front/38 rear. On a long trip (500km) at highway/freeway speeds I may add 4 psi front and back.

Interestingly, this question came up on the RR forum and John Robison (JE Robison Service - LR specialists) says there should be a differential between front and back. Don't run the same pressures. See http://rangerovers.net/forum/viewtopic.php...a376ba465240062

Robison claims the difference in tyre pressures provides stability. I had a rear tyre blow on the freeway (in the P38A). I heard it and wondered what the noise was. It wasn't until I saw the smoke that I realised it was my car. By tthe time I'd stopped, the tyre was shredded - not just missing a tread - and I hadn't even felt it. The P38A was rock steady.

Ron

<div class='quotetop'>QUOTE</div><div class='quotemain'>The difference in tyre pressures provides stability.[/b][/quote]

never heard that before. I had a blow out a few years back on the Putty road (Colo Heights end) on the right front @110km/h in a right hander.
Luckily it was the more lightly loaded side, and the 'fender tracked dead straight even under braking until the stop. It was an instant deflation, and I was driving on the rim. I was also running almost the same pressures front and rear. (IIRC @ 36 psi Bridgestone 235/85 MT's)

Generally, the tyre placard is a very good starting point, although the tyre placard for the 130 recommends 75psi in the rear in ALL conditions. (laden and unladen) If I ran that I'd have no tread in the centre of the tyres in about 5000km, the back end would be skipping all over the road, and I'd probably slash them to bits before that distance on our lovely gravel roads. Even with the OE Michelin XZL's, I started @ 50psi and dropped from there. Different tyres from OE also have differering constructions, with some being quite a bit stiffer or softer in the carcass, and so need a slightly different pressure to suit a given situation. Of course if the tyre size is different to OE, everything changes. Generally, a larger tyre (taller/wider) doesn't need as high pressures as a smaller one due to its greater internal volume, although this doesn't always hold true if the tyre uses a realtively soft sidewall/pliable case. More pressure may be needed here for support.

In road cars, I always ran more pressure in the front than the rear as there was much more weight over the front axle, as I do in our Patrol. (unless carrying a load) Any front engined race car I had anything to do with always ran more presure in the front than the rear for this reason. This was also borne out with lap times. Mid engined cars, even with their greater width/larger volume rear tyres always ran the opposite. e.g. Formula Fords run 17psi front, 19 psi rear hot pressures. Race tyre pressures are always checked hot, and adjusted accordingly. e.g. Cold days/weather, starting pressures may be higher, or a non abrasive track surface would use a higher starting pressure to achieve your hot optimimum running pressure. Differing suspension setups also require differing starting pressures, as they can work the tyre carcass differently, generating lesser or greater temperatures and consequently pressures.

Interesting fact on wet weather pressures. Any race car I ran that didn't use specialist wet weather tyres used much higher pressures in the wet than the dry
It didn't matter wether they were bias ply (Formula Ford, Historic Touring Cars, etc) or radials (production cars)
Any time I'd let the tyres down (at the request of a driver, 'cause everyone else was doing it) I'd be abused and we'd be as slow as everyone else. (I was accused by the driver at my first Historic meet with an XU1 of trying to kill him after setting the pressures where he insisted. He then proceeded to drive through the field in the second race and place, and he was a very cautious driver who hated the wet https://www.aulro.com/afvb/)
A couple of things are happening here. One is that the channels in the tyre are more defined with the higherpressure, the second and main one I think is that the reduced contact patch worked the centre portion of the tread much harder and actually was able to generate some sort of heat to generate grip. The tyres were always too cool after a race to actually check this with a pyro, but the fact remained that the cars were always much nicer to drive and much faster with silly high pressures.

It seems there are some discrepencies between what vehicle manufacturers recommend and what tyre manufacturers recommend. I find that if I run the front at around 28-30psi it is a lot harder on the turns and sluggish. Also find that tyres tend to wear. I usually run the fronts at 40 and rears at 42. I find light responsive steerin better, but it would be each to their own as long as it is safe. As previously mentioned tyre design and construction varies so refer to the tyre manufacturer ratings. Some tyres even say to run at 50psi.
At 2-30psi the front tyres actually look flat to me. :?:

<div class='quotetop'>QUOTE</div><div class='quotemain'>wow, I'm running much lower pressures in the 'fender with BFG MT 255/85's than the majority.
Generally 1/2 tonne+ in the back, fully loaded with bar work, winches, etc. 30-32 psi in the front 30-34 psi in the back, 26 psi on pure gravel.[/b][/quote]

As with Rick, I'm also running much lower pressures than the rest of you. BFG M/T 255/85s with ARB bar and winch on the front. Normally 32psi front and 35psi rear, unless really heavily laden, in which case I might bump the rears up to 40psi. On straight gravel, 25psi all round, and on sand, 18psi all round.


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

I spent many many hours and miles playing this game and found that running the placard trye pressures were the best settings...

definetly agree that the pressure difference between front and back makes a major difference to stability, slightly more so in the v8's than the tdi's but there is a very measureable difference.

Quote:

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Originally posted by incisor
I spent many many hours and miles playing this game and found that running the placard trye pressures were the best settings...

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[b]<span style="color:blue">running the recommended pressures will work best with the original tyres and setup of the vehicle.....

when accessories are added(more weight) and better off road tyres....
different pressures will be needed for best results......


there is no right or wrong for the vehicles once things have been changed from standard.....
all there is is a guide like you will find on this thread from different experiences......


so there is no real or simple answer....only a guide....</span>