Speeds above the reference speed
It is possible to operate bearings at speeds above the reference speed if the friction within the bearing can be reduced via a lubrication system that applies accurately measured quantities of lubricant, or by removing heat either by a circulating oil lubrication system, by cooling ribs on the housing, or by directing cooling air streams, see the section Methods of oil lubrication.
Any increase in speed above the reference speed without taking any of these precautions could cause bearing temperatures to rise excessively. An increase in bearing temperature means that lubricant viscosity is lowered and film formation is made more difficult, leading to even higher friction and further temperature increases. If, at the same time, the operational clearance in the bearing is reduced because of increased inner ring temperature, the final consequence would be bearing seizure. Any increase in speed above the reference speed generally means that the temperature difference between inner and outer rings is greater than normal. Usually, therefore, a bearing with a C3 internal clearance, which is greater than Normal, is required, and it may be necessary to look more closely at the temperature distribution in the bearing.