The Heckler

I'm planning to buy a Dura Ace 7800 cassette either in 12-21 or 11-21. For some reason the 11-21 is about $120+, and the 12-21 is $85. I currently have a Sram 1070 in 11-25.

Would I be able to buy a Dura Ace 12-21, take out the 21T cog and put in the 11T from the SRAM cassette that I already have? This is 10sp by the way.

I'm not a super cyclist, I just live in a very flat area and would rather trade the 23 and 25 tooth cogs for a 16 and an 18.

Chris_W

First, you need to know which cogs are mounted on a carrier together - normally the largest three are, and sometimes the next two on a separate one. Cogs on carriers cannot be changed individually, so no you cannot remove just the 21 tooth cog from either cassette. You can usually change the small individual cogs around, but it does slightly hinder shifting because the ramps and gates work better when next to the intended cogs.

stedalus

Like Chris_W said, the last three cogs will be mounted on a carrier, so you can't just slip off the 21T cog. In the olden days you could sometimes grind off the pins that hold the carrier together, but with 10 speed, the last cog sits out behind the freehub, so the carrier is necessary.

If for some reason you do try to move your 11T over, note that the lockring is special, so that needs to be switched too.