What is the effect of groove radii on the thrust capacity of a spiral retaining ring?

A radius at the bottom of the groove is often necessary for stress concentration reduction in the shaft, but it reduces the effective contact area for the retaining ring. The allowable thrust load $P$ must be derated if the radius $R$ exceeds $10\%$ of the groove depth $d$. The modified capacity is $P' = P (1 - \frac{R}{d})$. If a large radius is required for shaft fatigue life, a 'heavy-duty' ring with a larger radial wall or a square-edge shim must be used to ensure the ring does not climb out of the groove.