All bearing manufacturers' publish bearing product tables which list speed ratings under a given load condition. As of yet, there is no ISO standard for evaluating bearing limiting speeds and as a result confusion exists.

Bearing tables normally show two speed ratings, one for oil and one for grease lubrication. If integral contact seals are an option, the table will also list a speed rating for the sealed (and greased) version of the bearing. These are thermal speed limits.

When a bearing operates under load, heat is generated internally as a result of rolling, sliding and fluid friction. As the bearing speed increases, the temperature of the bearing also increases. If the bearing temperature exceeds certain limits, the efficiency of the lubricant falls drastically and the bearing will no longer operate in a stable manner.

Therefore, the maximum speed at which the bearing can continuously operate without generating heat beyond a specified limit is called the speed limit or allowable speed. Under this value and at the manufacturers specified load condition, the generated heat will be dissipated as fast as it is created.

The actual allowable speed of a bearing depends primarily on: bearing type and size; lubricant type and quantity; bearing load; bearing cage; bearing precision; and ambient temperature. These items should be reviewed in conjunction with to the published catalogue value.