Determination of thermally reliable reference speed is described in DIN 732-2 (draft). Calculation of thermal reference speed is based on heat balance data on the bearing. Thermally permissible service speed is calculated using the speed ratio from the thermal reference speed. The speed that is determined is achieved at the permissible temperature of the bearing for a concrete application. The thermally permissible service speed can fluctuate significantly from other limit speeds because the conditions only apply for very specific cases.