What causes a spiral retaining ring to 'Spiral Out' of the groove during high-speed rotation?

'Spiraling out' is a failure mode where the ring's centrifugal expansion causes it to lose its grip on the groove bottom. Once the ring is no longer seated, the leading edge of the ring can catch on a housing feature or be pulled out by vibration. The critical speed is $\omega_c$. If the operating speed $\omega_{op} > \omega_c$, the ring will expand. For troubleshooting, check the 'Free Diameter' $D_s$ of the failed ring; if it is larger than the original spec, it was either over-stressed during installation or expanded by centrifugal force. The fix is to use a 'Self-Locking' ring or a material with a higher $E/\rho$ ratio.