In order to achieve optimum racing brake performance and prolong disc life it is essential that the brakes operate at the correct temperature. In general discs should run at similar temperatures front and rear and from side to side, dissimilar temperatures will lead to varying brake balance.
Temperature balance can be checked as soon as the car stops in the pit lane using a Pyrometer such as AP Racing Pyrometer kit CP2640-24.
However a pyrometer reading is not a good indicator of disc operating temperature which decays rapidly with time when the brakes are not being applied.
Under racing conditions disc bulk temperatures should normally be maintained in the range 400°C to 600°C for best performance. Disc face peak temperatures may be higher but should not exceed the maximum recommended for the pad material being used.
An effective method of checking maximum disc operating temperature is by using temperature paints applied to the disc.
A suitable paint kit can be obtained under AP Racing Part No CP2649-1, this kit contains three 15ml pots of paint, Green (turns white at 430°C), Orange (turns yellow at 560°C) and Red (turns white at 610°C) plus thinners and three brushes.
|Material Safety Data Sheet (MSDS)|
|MSDS for Thermal Paint Kit can be downloaded Here|
When assessing brake temperatures it is important to complete several successive laps (5 or preferably 10) at race speeds and vehicle weight to allow temperatures to stabilise at a representative level.
Typically when running within the correct temperature range the Green paint (430°C) will turn throughout, the Orange paint (560°C) 50% to 100% throughout and the Red paint (610°C) turned up to 5mm from each brake face. If the Red paint (610°C) turns throughout, the discs are running too hot. Disc face grooving is also an indication of running too hot.
Circuits and drivers vary enormously in the amount of work they demand from the brakes and therefore the brake system has to be tuned for each circuit by adjustment of the cooling airflow. The temptation to over cool the disc should be resisted. The aim is to keep the temperature as stable as possible within the working temperature range. High maximum to low minimum temperature cycles are the enemy of disc life.