There is a direct link between temperature and pressure.
Look up the combined gas laws if you want the detail but very roughly, the pressure will increase by the difference between the temperature of the tyres before you went out and the temperature immediately that you come in. Temperature in Kelvin, that is, or Celsius +273.
So, if you go out with tyres at 10C (283K) and 1 bar pressure and come in with tyres at 38C (ie 28C hotter, 10% of 283K) then your tyre pressure will be 1 bar +10% of 1 bar (ie 1.1 bar).
There are a lot of reasons why this wont be exact. For a start, it takes no account of the expansion of the tyre, which will change for each tyre and with age and wear (the tyres get softer and expand more). Also any air you pump into the tyre is likely to contain water vapour which alters the formula.(Which is why some people use commercially dry air or nitrogen, So at least keep your air compressor drained )
It seems to be that kart tyres operate between 40C and 60C and a pressure between 1 and 1.2 bar.
Each tyre mix will be different.
In F1, they reckon that the difference between a bad performance and good performance on the same tyre can be less than 0.5 psi (0.034 bar)
Remember that tyres cool pretty quickly, so if you have a long run in to the pits, take the temperatures several times, so that you can calculate an on-track temperature (unless you have a remote tyre temperature sensor for your datalogger)
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Tyre temp vs pressure by 'Burton' (06 Jul 2010 @ 20:54)
