Cassette Question

I mix SRAM and Shimano cassettes with Shimano and SRAM derailleurs.

What I think is happening is:
1.) If the chain is dropping between the largest cog and the spokes, then a little tuning will fix it. But that's too E-Z. So it's got to be...


2.) If the chain is dropping between the inner chain ring and frame, then the chain may be too short for a 28 tooth cog. Going from a cassette with 26 large cog to a cassette with a 28 larger cog will force the rear derailleur to extend two links toward the crank. This extra tension is relieved faster when shifting from outer to inner chain ring in the front. Extra tension can also affect the lateral alignment of the rear derailleur and chain rings.

The solution depends on your rear derailleur. If the RD cage is long enough, or the data sheets list the cassette range given the chain ring sizes, then replacing your chain with one that is 2 links longer should solve the problem. Another way to tell if your drivetrain will accept 2 more links is to shift to small chain ring and small cog. If the chain approaching the bottom pulley makes contact with the upper pulley, then there is no more chain capacity.