Rules for dry tyres performance.
Grip is determined by mechanical grip, the friction between the rubber and the road; and Chemical grip, the grip caused by the tyre becoming 'sticky' with heat.
Mechanical grip is controlled by the size and shape of the contact patch, the bit of the tyre touching the road.
Chemical grip is controlled by temperature normally up to a maximum when the rubber starts to pull apart.
Because of the tyre shape if you underinflate the tyre, the tyre buckles (like when you put a tyre on the rim), if you overinflate the tyre the contact patch gets smaller. Most tyres seem to run best at about 1 bar (14.4 psi)
Most tyres seem to run best at between 145 to 160F (62 to 71C). The process of driving creates energy in the tyre, some of which is retained as heat. The heat increases chemical but also cause the pressure in the yre to rise. This alters the shape and reduces mechanical grip.
The idea is to drive so that the tyre heats up then stays at a roughly stable temperature and roughly stable pressure. (Obviously, the temperature fluctuates as you drive).
To test tyre pressures for a particular track:
Measure the tyre pressure and temperature in Kelvin before you go out on track. (degrees Kelvin = degrees centigrade +273)
Go out and do five laps. Measure the tyre temperature (or pressure) immediately. To convert the increas in pressure to temperature use the formula (initial temperatureK/initial pressure= second temperatureK / second pressure).
So if you go out with a temperature of 283K (ie 10C or 50F) and a pressure of 1 bar. and come in with a pressure of 1.2bar ( a rise of 20%) then the temperature will be increased by 20% (56.6K) to 339.6K (66.6C). 66C falls in the middle of the best range, it might be right for this tyre.
You also have a heat input per lap of 11C.
If your lap times show the tyres 'came in 'on lap 3 then went off, then you need to cool the tyres down (ie the best temperature is less than 66C) if they were still improving then the best temperature might be more than 66C and you need to heat the tyre up.
If you decide that the best temperature after 5 laps should be 60C then you need to set the pressure before you go out
In this case secondtemperatureK/secondpressure= firstTemperature/first pressure. (so 273+60/1.2=283/? so ?=0.876 bar). If your tyres are still at 10C the second time out, then alter the pressure to 0.87bar. If the tyres are hotter say 15C then the pressure on the grid is 0.89 bar.
Note that the amount you might need to change the tyres is very small, in this case 0.02 of a bar (0.3 psi). In F1 it has been found that a change this small can turn bad grip into good grip and vice versa.
That's the theory, Now all you can do is follow the ITPRO advice. testand measure, test and measure, test and measure.
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tyre pressures for Beccles Testing day saturday by 'HarryH1997' (28 Oct 2010 @ 0:21)
