Tyers for a Bristol 407

[irienz]

Tyre pressures increase with heat and the heat increases the harder the tyre is worked. On my race car, I look to set pressures cold (before the sun gets on them) and achieve a 5 lb lift in pressure at the end of a track session. If the pressure rise is less, the tyres have not come up to working pressure which means the pressure has been set too high for the conditions - I reduce the pressure to get more heat into the tyre. If the pressure comes up more than 5 lbs, the tyre is under-inflated for the conditions and, somewhat counter-intuitively, the pressure must be increased to stop the tyre overheating.

My race car is an Alfasud, a small front wheel drive saloon, on treaded race tyres (Yokohama A048s). I will commonly start with 26 lbs in the front and 17 lbs in the rear. The rear end sees little weight and does relatively little work so the low pressure is essential to get them up to working temperature. Ordinary road tyres do not have such stiff sidewalls and need more pressure on the track to stiffen them up and stop them overheating.

I run about 30 lbs all round on my 411.


Chris Browne
Auckland, New Zealand
irie@orcon.net.nz
Cellular: +64-21-617007