Tire Pressure
The air pressure in the tires is one of the most important things to get right. Starting with manufacturer recommended pressures is best, and then experimenting with lower or higher pressures. An important point to remember is that for example 12psi might be absolutely perfect during your first three laps but your times might quickly start getting worse (often a sudden .5 tenths per lap slower). This means that your tires were at the optimum pressure when you started but as tires heat up the pressure builds up and the tires will start underperforming when the pressure gets higher than optimum. Being fast right out of the pits is what you need for 3 laps of qualifying, but not for a race.
I find that a good way to find tire pressures that work is by looking at your times. If you are able to consistently drop your times by a tenth per lap for example over the first five laps and then your times stabilise or still improve slightly at a slower rate for the next 10 laps you have found good pressures for a 10-15 lap race. You can try slightly higher pressures until you reach the point where your times get worse after a few laps.
Generally You would use lower pressures for a long race, high ambient/track temperature, and when there is a lot of rubber on the track. For the opposite conditions you would reduce tire pressure. In wet weather the more water there is on track the more pressure you should run. On a drying track it is important to run low pressures in wets to prevent them overheating as much as possible, or if possible use an old set of wet tires that have been hardened and will be able to maintain grip on a drying track.
