[Adam43]

I thought the main reason for using N was to reduce the other gases in the tyre, especially water and CO2. However it doesn't eliminate the fact that the temperature and the pressure are always proportional.

There are separate and related problems here. Al of which have been mentioned above.

Firstly as the temperature of the tyre increases so will the temperature. PV=nRT (this is the ideal gas equation, but apart from a small deviation it works).

The temperature of the tyre is effected how it is used. It increases as it is driven. How it increases is effected by the shape of the tyre. However the pressure of the tyre effects the shape and the contact area! Complex? Yes.

Therefore a general knowledge of what is going on is needed, however in practice the fundamental theory is not that helpful.

One way of checking is seeing if your tyres are working well is checking the temperature difference across them. Making sure that the inner, centre and outer parts are working as much as each other. Having the same across the whole tyre is what a lot of people think is best, but some like a slight difference toward on edge. The pressure and camber required to achieve this will change for each circuit depending on how much straight there is to corner!

There is no wonder that tyres are described as a black art.

For all this talk we run the same pressure everywhere (we don't get a lot of practice to try anything! We have settled on something that is thereabouts). We run slightly lower pressures if it is hot! We might change if we feel the tyres going 'off' towards the end of practice, but track conditions change through the day too!

Experience is the key and it is hard to get quickly!