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HELP wanted

buckymfcbuckymfc Posts: 22
edited April 2010 in Workshop
Hi all,
its mr stupid again, can anyone please tell me why are rear mechs different lengths?? Im building a bike for the first time to do triathlons on and have 9 speed shimano bar end shifters, im looking to use possibly a 11-25 rear cassette but i dont know which rear mech to go for, i dont have a lot of cash as im unemployed and would hate to buy the wrong length mech and be stuck with it


  • gaspodegaspode Posts: 110
    it's related to the number of front chainrings - typically, a single will need a short cage, a double needs a medium, and a triple will need a long cage......
  • Monty DogMonty Dog Posts: 20,614
    ^ not quite correct: Short-arm is all you need - generally fine for a regular double chainset and a rear cassette with up a 27 tooth big sprocket. You only really need a long-arm with a triple i.e. broader range of gears to accommodate the bigger difference in chain length between the extremes of the drivetrain.
    Make mine an Italian, with Campagnolo on the side..
  • Hi buckymfc,
    I agree with Monty Dog. I would imagine that you are building a fast bike with a double chainset, go for a decent short cage, maybe even something used but in good nick. If your not building for fashion an older 9 speed shimano would work great. Back in the day I used to run my mountain bike (12-28 8 speed cassette and 24,36,46 triple) with a short cage 105 and it worked great. I would have only needed the long or medium cage if I'd wanted to use the smaller cassette sprockets with the granny ring.
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