Under Pressure

[spamanglenn]

I used to go to track days with 30 psi cold and come in with 38-40psi hot.Last time i had 32-33 psi cold and came in with 38 psi hot.The more air the less flexing of the carcass hence the less heat in the carcass means less psi increase.However the more psi means a smaller contact patch for a same given speed,means MORE contact patch heat.Either way the arse was hanging out after about 6 laps yet the the tyre pyrometer showed about 55-65c carcass temp??One important point i did discover was if a tyre at 40psi hot slides,its alot more sudden than if a tyre at 36psi hot slides, because of the smaller contact patch at 40psi.Coming out of a corner in 2nd with bridgestones 002 street compound(hot) felt like a slipping clutch. .front was good though.All tyres vulcanise(dry out) and lose their cold grip and upper limit grip first.So a pure road tyre has lots of cold grip so run street pressures on the street 38-42psi.As they get a bit older and have less cold grip perhaps drop them a little 36-38 to heat them up a bit more as your cold grip depletes.Road legal track tyres have alot less cold grip in their composition.Hence running 40psi on cold mornings wouldn,t be wise.36psi front and back would be a good starting point.It,ll turn a little sluggish for a while but it,ll come good.60 psi would have a contact patch of a mountain bike.Thats only for those who like mountn men. Glenn the Spa Man<i></i>