Probably a numpty question, but since I’ve only ever replaced rear mech’s in a like for like fashion, I thought I would ask the question.
Other than the obvious, as in the long is longer and the short is shorter and the Medium is somewhere in between the two, what’s the difference. Will a short cage mech work on a bike normally specced with a long cage mech?
Do long / medium / short have other benefits, I presume a short cage is a little less likely to be caught on rocks etc. but is that all it is?

Cheers.

rough guide but not the be all and end all

if it has 27 gears mtb cassette and you like to use them all then long cage

18 gears 2×9 then medium

9 gears 1 x 9 Short

there are exceptions though but generally stick to that and youll always be up and running easy enough. Remember to factor in chain growth , used to run a short cage ultegra on my 10 inch travel 10 monster and took me a few snapped mechs to realise it was the chain growing that was snapping em off

I tend to go on the largest cassette sprocket- over 27 teeth and its a medium cage, over 32 I go for a long, whilst also agreeing with the above post.

I knew I was missing something!
It now becomes blatantly obvious that the mech (cage) needs to be long enough to cover the full spread of the cassette in the full range of front rings.

Cheers guys.

yeah basically the mech is speced with a max range usually shown when your buying , this is the difference between the number of teeth on the biggest gear combo and the smallest gear combo …

AFAIK Shimano don’t even make a short cage MTB mech any more.

There never has been a short cage MTB mech. Road mechs come in the short variety, and only certain road models anyway.