Rear Derailluer short, medium and long

Ghuraba · 1 Mar 2011 at 12:10

Hi there

What is the difference between a short, medium and long rear derailluer? For example the Sram 9 has 3 to chose from. What difference does it make and why chose one over the other?

Speaking of derailluers is the SRAM X9 Rear Derailleur 9sp 2011 any good?

Thanks

Michael

ichabod crane · 1 Mar 2011 at 12:13

The cage length is related to the number of chainrings up front, Long Cage = 3, Medium = 2 and Short = 1.

[DOD]Asprilla · 1 Mar 2011 at 12:27

On a road bike it's to do with the size of your cassette. The cage is the bit that holds the two chain sprockets and so the bigger the cassette the longer the cage is required to stop the sprockets meshing with the cassette.

I can get up to 27t on a short cage, but any more and I'd need a medium cage.

Ghuraba · 1 Mar 2011 at 13:15

ichabod crane said:
The cage length is related to the number of chainrings up front, Long Cage = 3, Medium = 2 and Short = 1.

Forgive me for my ignorance but by chainrings do you mean the 3 different cogs at the front derailleur? If I have 3 of these I need the Long Cage rear derailluer?

Michael

ichabod crane · 1 Mar 2011 at 13:19

Ghuraba said:
Forgive me for my ignorance but by chainrings do you mean the 3 different cogs at the front derailleur? If I have 3 of these I need the Long Cage rear derailluer?

Michael

Yes

But you can get away with a Medium as I do.

ichabod crane · 1 Mar 2011 at 13:40

[DOD]Asprilla;18573252 said:
On a road bike it's to do with the size of your cassette. The cage is the bit that holds the two chain sprockets and so the bigger the cassette the longer the cage is required to stop the sprockets meshing with the cassette.

I can get up to 27t on a short cage, but any more and I'd need a medium cage.

I think MTB maybe different as the mechs come in standards of 7,8,9 or 10 to match the cassette.

Big Chris · 1 Mar 2011 at 13:46

ichabod crane said:
But you can get away with a Medium as I do.

Does that mean you can get away with a short cage if you only use 1 ring up front?

6thElement · 1 Mar 2011 at 14:00

Read this:
http://forums.mtbr.com/showthread.php?t=284688

[DOD]Asprilla · 1 Mar 2011 at 14:09

ichabod crane said:
I think MTB maybe different as the mechs come in standards of 7,8,9 or 10 to match the cassette.

Road mechs come in 7, 8, 9 and 10 to match the cassette as well.

The cage is essentially there to take up chain slack so the bigger the difference between your top and bottom gear the longer the cage needed. However, the longer the cage the more chance it has of getting damaged or pulled into the wheel and the shorter it is the more chance it has of being pulled into the cassette.

Your cage choice depends on both front and rear.

I'd never considered the chain rings because I've only used doubles before; triples are for tourers and pregnant women.

ichabod crane · 1 Mar 2011 at 14:22

Big Chris said:
Does that mean you can get away with a short cage if you only use 1 ring up front?

Essentially that is what most DH bikes run.

[DOD]Asprilla;18574086 said:
Road mechs come in 7, 8, 9 and 10 to match the cassette as well.

The cage is essentially there to take up chain slack so the bigger the difference between your top and bottom gear the longer the cage needed. However, the longer the cage the more chance it has of getting damaged or pulled into the wheel and the shorter it is the more chance it has of being pulled into the cassette.

Your cage choice depends on both front and rear.

I'd never considered the chain rings because I've only used doubles before; triples are for tourers and pregnant women.

I have just always assumed from how the manuals read that length of cage is related to number of chainrings

Big Chris · 1 Mar 2011 at 14:46

ichabod crane said:
Essentially that is what most DH bikes run.

Interesting... I've realised that I don't ever shift out of middle ring up front so was thinking of binning the other two and the shifter and going 1x10 (when I can afford all the bits, and my Heckler frame).

Short cage 10sp rear + 32 up front with a chain device = win?

ichabod crane · 1 Mar 2011 at 14:58

Looking at that mtbr link it does look more complex than my original reply, but I think they are over complicating it to make themselves feel smart

So I will stick to what I know works for me

Big Chris · 1 Mar 2011 at 15:36

Yeah I got lost about half way down so I'll just take your word for it, it'll either work or it won't!

mistercrabb · 1 Mar 2011 at 21:43

To confirm, it does depend on the rear cassette too. The Saint short cage dérailleur (for example) is only compatible up to a 28 tooth cassette.

Chain growth on full suspension bikes is also a problem. I fitted (fit?) a Saint short cage onto a 26t cassette on my TR450 and it was quite hard to keep the chain tight through all the gears without shortening it too much to run in the easiest gear (when fully compressed). However it does work safely

Ghuraba · 2 Mar 2011 at 14:29

I just rang Halfords out of interest to see what they said and he said that any size Sram X9 rear derailleur will fit my bike, Carrera Fury 09, irrespective of 1,2 or 3 front cogs. He said the only reason there are 3 sizes is how you use the bike. I rang about 5 different branches and not one new what size derailleur was on the bike. He said a meduim or long most likely.

Was he talking cobblers?

mistercrabb · 2 Mar 2011 at 18:17

Looking at a picture of your bike, I would say it's a medium. However, I may be wrong.
Either way, it's definitely not a short cage and I wouldn't particularly want to try a short either. Among other things your chain will be slacker because of the shorter arm.

If in doubt, take it along to a real bike shop (not halfords!) and ask their advice, they will definitely be able to sort something out for you.

To answer your original question, yes the X9 is a very good dérailleur, but it does need to be set up carefully, again something you might prefer to get a bike shop to do if you haven't done it before.