Hi DirtRacer, I am still on the first set of bearings I fitted so I can't give you a time frame as yet. My truggy is pretty hard on clutch bearings (maybe it's my driving !!) and I was changing them after maybe 5 tanks of racing. I tried several brands but they all seemed to get pretty scratchy and/or start to come apart after this time. I have done one race meeting of 3 x 5 min heats and a 20 min final, plus some thrashing around home on the MM bearings and they still feel like new. No play in the clutch bell either. I also fitted a set to my buggy with a brand new Go Tech 5 port for run in. I am up to 13 tanks of stop start figure of 8's which is pretty hard on clutches and again the bearings still feel like new. I am relatively new to this game so I don't really know how long a set of clutch bearings is meant to last. Depends on how hard you drive it and how much dust etc you are in I guess, but going on my limited experiance I can safely say that the MM bearings are lasting much longer than the others I have tried for sure