Tyre Pressures

Nice name! What next? Goodyear Hobo? Michelin Wino? :)

These will be used mainly for road

If my 90 was anything to go by 28f 35r on road and let down to 18 all round for off-road work.

They over-inflate them to seal the bead to the rim - you shouldn't ever need more than 28f 35r on road and lots less off-road to improve traction. And of course the tyre fitter doesn't know what vehicle they are going on - could be a fully laden 101 for all they know! :)

I'll agree with that. I got a complete set from Bronco for Charlottes Discovery - they sent the wrong ones at first, but hot-swapped them very (very) quickly, to my complete faction. Mine were overinflated but they did say to check the pressure once on the vehicle. (Even if they didn't, it's common sense).

Yeah, in which case the pressure should be 28 / 26 - but then again, I have a lot of air volume in my fully laden 101 :-)

Martyn

Many thanks for that. I thought via common sense that they were too high, but being 'large' tyres I was not 100% certain, and thought that someone her would put me right. Thanks all once again.

Dave

On or around Sat, 04 Oct 2003 20:00:46 GMT, "Exit" enlightened us thusly:

on the 110 and disco, I run equal pressures, unless carrying heavy weights. The disco on 205R16 tyres gets about 36 in each, while the 110 on

31x10.5R15s gets about 34, used to run the Pirellis softer than that, but the nankangs on it now seem to want a couple of PSI more - was getting some odd tyre wear which I eventually decided was due to slight underinflation.

put the back end of the 110 up to about 46 for heavy towing with the big trailer, as it misbehaves otherwise; mind, next time I'm gonna play with the loading and try to get it better balanced, I reckon most of the bad behaviour is down to too much noseweight.

On or around Sat, 4 Oct 2003 21:43:03 +0100, "Foxhunter" enlightened us thusly:

mostly, larger tyres actually run slightly softer, rather than harder.

I have some Goodyear MT/R 235/85R16's on my 90. I started out with 28psi all round. The road manners were bloody awful to put it politely. I used a tyre pyrometer to check the tyre temps. As a result I'm now running 35psi all round on the road and 25F 22R off road which fits nicely with ARC regs and all :)

Pyrometer? Does that involve setting fire to the rubber?

Alex

A point in relation to a recent thread on Tyre Pressures. We all know that off road you use the pressure that works, but as most of our milage is on road we should be able to use the correct pressure to prevent under\overinflation related premature wear.

Accepting that 4x4 users will generally run tyres other than the standard issue eg my current Bridgestone 31x10.5 or my future 16x9 Mabors, why can the manufactures not simply supply a table of axle load - Tyre Pressure.

I am in South Africa and I could easily determine my axle weights on any of the local weighbridges, and those who tow regularly could also check their towing axle load. This way you would be able to determine the proper inflation for a given axle load without resorting to ocassionally checking tyres for signs of over/under inflation by which time it is too late.

I have searched most of the manufactures websites for such data to no avail. Since 4x4 owners tend to invest quite a lot of loot in tyres, I think this info should be more easily available. In addition following the not too distant Ford Explorer/Bridgestone debacle I would have thought that manufactures would make more effort to give the public info on correct operating proceedures for their tyres.

Am I being too simple minded?

Regards Fanie

Doubt it

As you point out the on road pressures are more critical. However, the best tyre pressure will not be simply load related for a variety of reasons. Tyre grip on hard surfaces depends on pressure to some extent, and particular vehicles may require slightly different front/rear grip to avoid dangerous handling, for example. As the critical factor for the tyre life and survival is temperature, pressure will need to vary with ambient temperature - for example the pressure needed in driving on an autobahn in a German winter will be lower than on the Stuart Highway in summer, probably by a considerable amount. Then you have to balance ride comfort against tyre life - and here the vehicle manufacturer may well have different priorities to the tyre manufacturer, and again the driver's priorities may be different again. The type of road surface will also influence the temperature rise, and hence the required pressure. Interestingly the reccommended pressures in the Australian supplement for my

110 are higher by 5-10psi than in the original handbook, and vary with both speed and load from 35/35 to 45/65 - for the same tyres as the original handbook. For tyre sizes that are not approved by the vehicle manufacturer (and they may not approve them simply because they have not tested them, or may have good reasons for not approving them), tyre manufacturers are reluctant to publish any information that suggests they know better, as this could be taken as assuming responsibility for this use. JD

Point Taken, and well made. However consider that my handbook recommends

1.9 bar front and rear (not too sure of the psi) for the standard LR tyres. On my 31x10.5 i have been running at 2.5 bar front 3.0 bar rear which is way above the standard recommendations and my tyres are a lot wider than the standard issue.

The only time I go as low as 1.9 is when I am on the beach towing a boat. The point is that I have taken advice from Mates running similar tyre/ vehicle combos and have come up something very different from the manufacturers recommendation. The nett result is expensive tyres that were wearing prematurely due to overinflation.

If we accept that the public are not complete cretins (a safe assumption?) surely it is possible to provide some indication of the correct inflation pressures bearing in mind (average crusing speed, axle load, ambient temp. Again this could simply be a matrix with a few more columns for temp ranges etc, speed, load etc.)

Regards Stephen

On or around Tue, 07 Oct 2003 06:45:26 +1000, JD enlightened us thusly:

that is interesting. One thing I've never understood was the perpetuation of the 28 lb in the front recommendation - this wasn't far off for cross-ply tyres, but all radials I've had look and wear significantly under-inflated at that sort of pressure, and when not carrying heavy loads, I've formed the opinion that the various landy-things work much better with almost-equal pressures front/rear.

am I right in thinking that the latest recommendations have gone away from the 28/35 that dates back to the series II on crossply tyres? ISTR the ones for more-recent Range Rovers are more even?

as with the infamous firestone/ford row...

On or around Tue, 07 Oct 2003 07:20:35 +0200, fanie enlightened us thusly:

running at about 2.4 bar on tarmac here, with those size tyres on a 110. 34 psi, give or take - that's what they get inflated to when I bother to check.

This is for Nankang wide conquerors. previously, I had Pirelli Scorpion AT, and they were happy at about 32 psi. The nankangs were showing unacceptable edge wear 'til they got blown up a bit more.

1.9 front sounds like the 28 psi previously mentioned, which is apt to be too soft IMHO with almost any radial tyres, for tarmac use.

nope.

yeah, but there are a lot of variables as you've just noticed. You have to add pressure in theory for going faster, and for different loads, and different temperatures. At best, the pressures in the book are only guides

- you develop your own "list" based on experience. For example, for towing my big trailer loaded with hay, experience taught me quite quickly that 34 psi was nowhere near enough in the rear tyres, spontaneous weave at about 43 mph on the straight and level. upped the pressures next time to about 38, this made it better, and the most recent time to 44, which was better still.

but the book doesn't know I've got a 20' trailer which, loaded with hay, is transferring a fair amount of weight to the towing vehicle. Next time, I may try loading it differently to get less noseweight - I did this when carrying the 110 on it, towed by the disco - with a vehicle, it's easy to adjust the load to get whatever noseweight you want, this towed nicely, although I wasn't in a hurry and didn't go over about 35 - all-up, the trailer was over 3 ton...

In article , Austin Shackles writes

I've been quietly reading this thread and worrying. My Haynes manual says, IIRC, 28F 32R. I tried this and found it WAY too low. Currently running 40 all round, unladen (110), on Goodyear radials, which feels nice.

Am I being silly?

Regards,

Puzzled of Bristle