rear mech lengths

[topshifter]

how comes back in the day you could run short cage mechs on triple cranksets but now your told they will only work with double ring set ups or single ring set ups? i mean all i ever seem to remember was triple ring bikes, and some were using short cage mechs, is it to do with the cassette speeds increasing with more rings :?

 

[feetabix]

The only thing that has changed are the ratios on the rear block......12-28 was the norm but 11-34 are not now uncommon......I think it's part of the general move toward 2x10....

 

[We_are_Stevo]

If the top jockey wheel/chain clears the big cog on the back then you can get away with a short cage mech. so that's really your only consideration - I'd use them every time if they came up for sale often enough for me to catch one...

 

[hamster]

The other consideration is whether the mech can take up the slack. The chain has to be long enough for a big-big combo. While you may not use that in anger, the chances are that sometime you'll select that gear, which usually stuffs the mech though the back wheel.

 

[bm0p700f]

It depends on the difference in the number of teeth in the front chaing rings and diff in the number of teeth in the rear cogs. Add the difference together and that is the range. The rear mech itself should have its max capasity on it. Therefore it should be easy to match the mech to your choice of cogs.

Shimano
Long cage ~45T capacity
Medium cage ~ 33T


SRAM
Long cage = 43T
Medium cage = 37T
short cage = 30 T

Use the shortest mech you can get away with as the above figures are concervative. I.e you can use a medium cage mech on drive trains with a higher range than that stated above.