Limiting speed values for instrument bearings are almost impossible to determine. However, generalizations may be made.
Bearing size: Highest speeds may be obtained with the smallest bearing. However, extremely small miniature bearings usually have a thin, weak retainer and their maximum speed is less than medium-size miniatures.
Load: Limiting speed is directly affected by the magnitude of applied load. Heavy loads result in a decreased speed capability. Use of a preloaded pair of bearings also decreases allowable speed.
Ring rotation: Inner-ring rotation gives higher speed capability. If the outer ring is rotating, limiting speed must be reduced by about one-third.
Retainer: Phenolic (and some other nonmetallic materials) — very high speed; crown (hardened steel) — high speed; ribbon (loosely clinched) — low speed; full race — moderate speed; spacers (PTFE) — very low speed.
Lubricant: Stiff, mineral-oil grease — high speed; soft, synthetic-oil grease — moderate to high speed; soft, silicone grease — low to moderate speed; mineral oil — high speed; synthetic oil — moderate speed; silicone oil — low speed.
Lubricant method: Oil impregnation and grease pack — excellent; oil impregnation — very good; grease pack — good; minimum oil — fair.