Calculating tyre pressure ?

This will calculate a pressure based solely on the tyre manufacturer's ideas of what their tyres will stand. It will probably give a higher pressure than you really want - I'm also not sure that pro rata is the way to go either.

Tyre pressures as recommended by the manufacturer are not calculated - they are worked out by trial and error during testing and are a compromise between comfort, handling and tyre life. Too low compromises tyre life and usually handling, too high will sacrifice ride comfort and often handling. JD

Trouble is LR dont give figures for 235 85 16's on a 110 and they dont know what they should be ( I phoned them )

you could run on the pressure for the narrower tyre 225 ? this will give that slight increase that most of us seem to run and adjust to taste if you find it too firm or notice increased wear in the centre (unlikely IMO). or Dunlops recommendation 1.9bar 28 psi (F) 2.4 bar 35psi (R) load index

104-116 (dunno what that is )

"Contrary to popular belief, tyre pressure is not determined by the type of tyre or its size but upon your vehicle's load and driving application i.e. speed"

quoted from

And these people make the tyres! JD

This is exactly what I have always run them at, but I am intrigued to know the collective wisdom and the "correct" pressure

Yep. And most vehicle manufacturers quote pressures that are too low in the interests of less road noise and better ride. The whole Bridgestone/Ford SUV debacle in the US stemmed from this combined with a less than optimally made tyre.

Another change that complicates things is that a lot of vehicle manufacturers are still remembering the days of cross ply tyres which had a much stiffer carcass and thus needed less pressure to handle well and stay cool in use - many of the designers don't seem to have grasped this change.

I saw a new set of pressure charts from one of the large tyre manufacturers (can't remember which one) a few weeks ago that was showing pressures about 15% higher across their entire size range than any similar charts I have seen in the past - so there may be a bit of realism creeping in to the industry.

I've fitted/sold tyres for most of the last 20 years (until I left the automotive industry) and somewhere between 10 and 20% greater pressure than the vehicle manufacturers suggestion is a good rule of thumb. As an example my wife's car is running 34/32psi front/rear (as opposed to the 29/27 on the placard) and after 50,000km the tyres are worn perfectly evenly. The cornering is a lot sharper and it runs more nicely on cambered roads. The only downside is a noticeable increase in road noise.

IMO (from experience with my own vehicles) 235/85R16's are happy with about 32 to 34 psi all round if you're not heavily laden. Give these pressures a try and see what you think of it's stability and cornering.

An interesting comment on this is that my 110 has an Australian Supplement to the owner's handbook. As well as covering special local variations such as different engines in some models, it tells you to ignore the tyre pressure recommendations in the owner's handbook and provides a new table, which is copied on the vehicle placard. This lists pressures well above the originals, minimum of 35/35 unloaded at speeds up to 100kph, going up to

60/65 at maximum weight and speeds over 120kph. Tyres type and size specified is the same as in the UK handbook. And this was in 1986. JD

Hi,

Is there any chance of getting a scan or details of the tyre pressure chart you mention, it would be very useful for us all I think,

Thanks, Andrew

(1986 110 V8)

JD wrote:

Tyre pressures from Owners manual Australian Supplement Part No TP 1107 A for Landrover 110 dated 2/85

Load Up to 105kph 105-120 Over 120

up to 0.5 Tonne 35/35 45/45 50/50

0.5 to 1.0 35/45 47/55 55/62 Over 1.0tonne 40/50 50/60 60/65

Pressures may be reduced by 4psi for crossply tyres

Presure may be reduced by 15psi for limited cross country operation.

I have not given the pressures for the 6x6 as these are rare outside Australia (and pretty rare here too!) and have only given pressures in psi.

Hope this helps JD

Thanks alot! - as you say they are consistantly higher than "normal" recommendations.

Next problem is trying to find an accurate but not silly money pressure gauge.

Cheers, Andrew

JD wrote:

Seem to recall there's some law/ruling that tyres must be inflated within

2lb/in^2 of the manf recommended.

For what its worth, I run a 200TDi 90 on crossply Mud Pluggas (SAT clone). As a main use of the vehicle is RTV trials I leave the tyre pressures at 25psi all round as this gives me a margin over the 22 psi min pressure for trials. I have no problems with road holding or tyre wear. They are wearing evenly and look like they will probably do around 20,000 miles before they're road illegal, not that they'll be much good off road by then. The only problem is the noise (no carpets or other sound proofing) and the feeling of running over bricks at slow speeds. They towed the caravan up to the Nationals and down to Newnham at 60, competed, then home again all at the same pressure, no trouble.

Gordon

On or around 16 Aug 2006 04:22:43 -0700, "gordon" enlightened us thusly:

I imagine that's about right for a 90 on oversize crossplies, I'm assuming that you're on 7.50s... crossplies work at lower pressures.

Yep and they also are responsible for this

which sort of explains how much they actually knowDerek

I often have a set of 7.50x16 SATs on my SIIa - I find that raising the fronts to about 28psi significantly improves the steering response on-road.