just another gosling
Join Date: Feb 2007
Location: Everett, WA
Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004
Mentioned: 8 Post(s)
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I go through middle chainrings on my Ultegra triple as fast or faster than the cassette, just because I tend to stay in the middle and move the chain around in back, spreading the wear. YMMV
Terminology: you're not breaking cranksets, you're wearing out chainrings.
Before you wear out a chainring, you're wearing out chains. Lube your chain a lot more often. Every 100 miles is good and after every time you ride in the rain. Use a good bike chain wet lube. Clean off excess lube and gunge with a rag after lubing.
Check your chain for wear and replace it before it's worn out. That will cost money, but so do chainrings and cassettes.
The mechanic is technically wrong - you don't have to replace them together. You just have to replace what's slipping and replace the chain at the same time. Then if the other end slips with the new chain, you'll have to replace it, too, but you won't know that until you replace the chain. It's just easier for him to replace the ring, chain, and cassette all together and have it all work when it leaves his shop. Otherwise it might not.