I die my sprocket carrier ones at high 20's (miles) but only due to them feeling notchy during a service. The wheel bearing had play in them at high 30's. You can tell by holding the wheel at 10 o'clock and 3 o'clock and wiggle it while sitting at 90 reg to bike. Any play at all and change them. Also if the wheel is off stick your finger in the hole and turn the inner race. If you feel any notchyness change them.

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