Chain length?

Gary Sinclair

If I'm currently running 11/25 shimano, could I squeeze a 11/28 without making the chain longer, or would it pull too much on the mech?

Gary Sinclair

And will it be ok on a 7900 mech?

andrewc3142

If I'm currently running 11/25 shimano, could I squeeze a 11/28 without making the chain longer, or would it pull too much on the mech?

Should be OK, just, probably. Suck it and see. Assuming it's OK, when you next change the chain perhaps worth setting the right length.

Probably best, though, to change the chain at the same time as the cassette.

Everything you ever need to know about chain length: http://bicycletutor.com/calculate-chain-length/

And will it be ok on a 7900 mech?

Just about, yes, although at the limit.

FWIW you might find 12/27 does the trick with better spacing between shifts.

chris_bass

best thing to do is give it a go, it'll either work and your good to go or not and you'll need to replace the chain which you are considering anyway.

once you have the new cassette installed, carefully try shifting to the largest sprocket whilst in the big ring whilst off the bike (I know cross chaining isn't advised but you want to know if you do it isnt going to rip the mech hanger off!) and see if it shifts ok and that there is still a slight bend in the rear mech.