Rear Derailleur size

lochindaal
lochindaal Posts: 475
edited March 2009 in Workshop
I have damaged by rear derailleur on my bike and want to replace it.

I have a compact 50/34 with a 9 speed rear. I have seen short cage and long cage advertised. Which is the right one and what is each supposed to be used for.

Thanks
Tri Coaching
https://www.h3otriathlon.com

Comments

  • John.T
    John.T Posts: 3,698
    Shimano?. If so and your cassette has no bigger than a 27 cog then a short one is fine. Just set the chain as long as possible.
    My Fleet.
  • maddog 2
    maddog 2 Posts: 8,114
    what John said
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • lochindaal
    lochindaal Posts: 475
    Thanks, yes it is shimano.

    Would you mind explaining the theory for future reference

    Cheesr
    Tri Coaching
    https://www.h3otriathlon.com
  • John.T
    John.T Posts: 3,698
    Basically a long cage mech is for a triple and a short for a double. You can use a long cage on a double, it just does not look as good. The longer cage is to take up the chain slack with the larger range between the big/big and small/small gears. Typically 37 teeth for a triple against 31 for a double.
    My Fleet.
  • maddog 2
    maddog 2 Posts: 8,114
    some compact scenarios do, theoretically, require a long cage if you want to access all possible gears but in practice a short cage is easily good enough, and has clear benefits (weight/looks/shifting)
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer

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