Just trying to find the ideal tyre pressures for my middy - is there a formula for calculating them or is it just trial & error?

For example it weighs 800kg with a 60/40 split (60% to rear) and I'm on tyres - front – 205/40/ZR17 - Rear – 245/35/ZR17

Any help would be appreciated

a lower tyre pressure gives more grip because the tyre is less Round/more flat
sow the touching surface is bigger.

the ideal tyre pressure is that one listed on the tyre (tyre wise) grip wise i think its trial and error..

Tks

Tyred temperature guage, if the temps are even across the tyre then the tyre is as square as it can be.

Every tyre has a maximum inflation pressure stamped on the side somewhere. This is the maximum pressure the tyre can safely achieve under load. It is not the pressure you should inflate them to.
- how can it be when the loading weight could be anything between 100kg and 500kg?

I have used an IR thermometer and get roughly even temps right accross the tread so I can't be far out at 20psi all round. I would be interested how others have arrived at their ideal pressures though.

[Edited on 10-4-07 by RazMan]

The pressure stated on a trye of approx 2 bars is the best working pressure for suchs tyre! if the load increases to compensate its adviceable to add a bit of air to the tyre.

Tks

The tyre is an important part of the suspension of the car, and the pressure should be lower on a lighter car. I don't buy tks theory about grip - but am sure the opposite is true on a wet surface!!!
A lot of the 'bling' 7's have low profile tyres AND rock hard suspension - the low profile tyres will have high pressure to protect the rims - the ride must be awful!!!!
cheers
Bob

I agree Bob - if the loading increases then the pressure must also. Therefore if my 1.5 ton tintop and my 800kg middy both use the same size tyre, the tin top must run higher pressures to achieve the correct footprint.