Operating clearance
Betriebsspiel
Operating clearance is the internal clearance that actually remains in a mounted bearing under operating conditions. It equals the initial clearance minus the reduction caused by fits — inner-ring expansion on an interference-fitted shaft, outer-ring contraction in the housing — and minus thermal effects when the inner ring runs hotter than the outer ring.
Most applications aim for a small positive operating clearance, which favours load distribution, friction and noise. Excessive clearance shrinks the load zone and raises noise and rolling-element stress; uncontrolled negative clearance causes preload, heat build-up and, in extreme cases, seizure. It is managed by selecting the appropriate clearance class; deliberately negative clearance is called preload.