It is recommended to set your tyre pressures when the vehicle is cold, because the pressures will then be correct for the majority of the time that the vehicle is in use. Although a cold start will mean that the tyres are potentially below the optimum setting if they are set to the minimum recommended pressure, the period of time for which this is the case is relatively small. We would not suggest overinflation because this would mean that for the majority of the time that the car is in use the pressures will be above the recommended level, which could mean increased wear and poor performance. A tyre that is a few PSI below the recommended level for a few miles is of little concern.