What causes the inertia ring on a stock damper to move on a high performance street application?

In a stock damper, inertia ring slippage is usually due to deterioration of the rubber strip. As the stock damper ages, the rubber strip begins to crack and lose its grip, in essence it becomes "overworked." Also, rubber is a poor dissipator of heat. The more severe the crankshaft vibration, the more heat builds up. This causes the damping characteristics to change, which could lead to damper failure over time.