Body 1 (ball) Body 2 (race outer ring)
 Young's modulus E GPa GPa
 Poisson's constant v
 Radius rx 10-3 m 10-3 m
 Radium ry 10-3 m 10-3 m
 Lubricant viscosity η0 Pas
 Viscosity pressure coeff α 1/GPa
 Number of balls z
 Rotational speed n rpm
 Bearing load P N
 Effective Young's modulus E' GPa
 Effective contact radius R' 10-3 m
 Semi contact radius a 10-3 m
 Semi contact radium b 10-3 m
 Mean contact pressure pm GPa
 Max contact pressure pmax GPa
 Viscosity number L
 Load number N
 Film height number H
 Couette flow film thickness hc 10-6 m
The lubrication regime in which the bearing operates depends on the rotational speed. At low speed Boundary Lubrication prevails (hc/Ra<1). Representative values for the Ra-value of the ball and raceway are Ra=0.001 and Ra=0.1 μm respectively. It follows that hc>0.2 results in full film lubrication (EHL: hc/Ra>2). This situation can easily be considered by measuring the electric conduction over the inner and outer ring of the bearing (EHL-high electrical resistance, BL-conduction)