Rumour has it (ie: the manufacturers won't confirm it) that kart tyres get maximum adhesion at between 60 and 65C, thats the temperature of the water in a central heating system.
Generally it seems that the pressure at that temperature should be around 1 to 1.2 bar Different karts, different tracks and the lack of instantaneous pressure sensors make it difficult to judge the 'best' pressure.
We know that tyre temperatures and pressures go up and down just as much and just as quickly as your cylinder head temperature, so the problem with 'pit lane' measurement is how long the pitlane is and how quickly did you enter it. (If you were at racing speed entering the pit lane, the stewards / pit marshal / practice supervisor should be having a word with you).
Heat a bucket of water to 60C. Put the tyre in, leave it for 15 seconds. Take it out, put it on tarmac and measure the temperature drop every 5 seconds. Do it again, rolling the tyre around on the tarmac.
Measure the air temperature and the temperature of the tarmac.
Now you know how much the tyre loses heat over the time it takes between racing speed and stopped.
The pressure will change in proportion to the change in temperature in Kelvin. (add 273 to Celsius).
If your tyre pressure is 1 bar at 10C before you go out, and the temperature is 38C after, ie change from 283K to 311K (a rise of 28K or of pprox 10% of 283)then the pressure should be 1.1 bar (a rise of 10% too).
Note that it is track temperature that is important. One day I measured the air temperature at 32C (90F) but heatsoaked concrete (and black tarmac can be hotter) at nearly 60C. Dont measure tyre temperature in your pit under the awning! Just last weekend when half the kart was in the sun and half in the shade, the tyres in the sun were an extra 0.1 bar higher in pressure. They had all been set the same in the shade. But then the water temperature just sitting on the grid was 24C before the engine had been started.
|
|
yet another noob question about tyres... by 'Darkcat' (07 Apr 2009 @ 23:41)
