I'm going to need to replace my rear mech soon (SRAM X-9) as its pretty worn after 4 years heavy use and some big hits.

I'm currently running a long-cage version. Would swapping to a medium or short cage version work just aswell (but have the benefit of being less exposed to hits?).

Cheers.

shorter cage just limits the length of chain you can run and thus the difference in front cog/rear cog that the mech will cope with.

If I got 4 years out of my old mech I'd be replacing like for like, to be honest.

To answer the question – Yes you can

The advantages are that it's slightly less likely yo be caught on rocks, and a it's a bit lighter. SRAM make a medium cage which is perfect for just about anything.

i ahve a medium x0 for sale if you are interested. brand new in box

Medium cage might be the way to go then, cheers.

The cage length is a function of tooth difference, not frame size/type/construction.

Find out how many teeth your smallest chainring has and how many the largest has. Subtract one from the other.

Do the same with your cassette. Add the two figures together.

This gives you a T number. A high T number needs a long cage, a low T number prefers a short cage, medium = medium.

Check with the manufacturer of your intended mech for the T number it can cope with. The max T number used to be engraved on the cage, but I haven't seen that for a while.

Great bit of advice on calcing whether you need short/med/long – one question does this still work if running a single chainring up front (as obviously it gives a value of 0…)

I''ve got a 36 single with 11/34 out back. I'm thinking I could get away with a short cage.

Interesting question. Thing is about cage length is its ability to wrap the "slack" chain. If you have a single front cog, then you are only going to get a small amount of slack, so yes, I reckon you could have a short cage. Obviously you would have shortened your chain down so that you're running the minium length necessary. Maybe people don't do this any more. I like to shorten my chains – lighter and faster changes (how sad am I?) 😉

Chain has been shortened as much as I dared 🙂

Thinking it is only a matter of time before the derailer is broken so when it gives up the ghost was going to try a short.

That T number thing is interesting.

as karin of 9 says, it's to do with the cassette teeth not the frame.

If you have say 11-34 then you will struggle with a short cage but if you have 11-32 you may just about get away with it.

The cage length is a function of tooth difference, not frame size/type/construction.

Find out how many teeth your smallest chainring has and how many the largest has. Subtract one from the other.

Do the same with your cassette. Add the two figures together.

This gives you a T number. A high T number needs a long cage, a low T number prefers a short cage, medium = medium.

Check with the manufacturer of your intended mech for the T number it can cope with. The max T number used to be engraved on the cage, but I haven't seen that for a while.

Or alternatively, just fit a medium cage because I know it's fine for a 3-ring 11-34 cassette set up!
🙂

on an HT. be wary of expecting med to cope with longish travel and all those gears…

Does it not also depend on wether and what type of full sus or HT you are running – i.e. chain lentgth on a double bounce is max to max and 2 links but on a HT poss get away with sl shorter?

wot tracknicko said – careful if your rear sus "grows" the chain significantly

Yep, if a medium cage always worked perfectly with a triple/11-34 they wouldn't make long cage mechs! It's not that straight forward.

on an HT. be wary of expecting med to cope with longish travel and all those gears…

Spesh Pitch Pro supplied with medium cage X9, 22,32,44 rings 11-34 caseette. Works fine. In any gear. Long cage not needed.
🙂