Which rear mech

ermintrude
ermintrude Posts: 514
edited February 2009 in Workshop
I want to swap my 12-26 cassette for an 11-28 would the same rear mech work ? (front is 50-34)

Comments

  • maddog 2
    maddog 2 Posts: 8,114
    Shimano?

    9 or 10spd? or 8 for that matter...

    budget?
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • ermintrude
    ermintrude Posts: 514
    Shimano 10-sp, budget - well don't mind replacing rear mech etc. if needed
  • John.T
    John.T Posts: 3,698
    You would need the longer GS mech. Yours would just take the 18 cog but can not take up enough chain to cover the range. Shimano recommend a max of 29 teeth and you would have 33. The short mech will take 31 teeth with carefull chain length set up.
    My Fleet.
  • andrew_s
    andrew_s Posts: 2,511
    Yes, it will work.

    The extra 3T range may be pushing the capacity, but exceeding the capacity only really matters if you select the smallest couple of sprockets with the small chainring. You shouldn't really be doing that anyway, and all that happens if you do is that you'll get extra rubbing noises and may possibly be a little more likely to drop the chain.
  • John.T
    John.T Posts: 3,698
    If you make the chain long enough to be safe on big/big (you will forget and hit it one day) the chain will be so long you will probably loose all tension on at least the top 3 cogs, maybe more. And it is still a lash up. Put the proper mech on and be safe. You will be able to use all your gears. OK, avoid the big cross over ones but they are useful sometimes. I often use small/small for short distances to avoid changing rings and have used big/big when I miss judged a hill or my legs. I payed for them so I use them.
    My Fleet.
  • dombo6
    dombo6 Posts: 582
    Yes it will work. I ran 11-28 on a standard 105 mech with 52/39 up front. The comments re big/big combination are irrelevant as you rarely use this gear. The 34x19 gives the same gearing and once you've worked your way that far up the cassette you'll likely be on the small chainring anyway.
  • John.T
    John.T Posts: 3,698
    52/39 is not the same as 50/34. 3 teeth is a one and a half more links. The coments re big/big are relevant. You say you RARELY use it. If the chain is not long enough you will only use it once and then not for long. I know 50/19 and 34/13 are the same gear (69") but I sometimes need 34/12 (74") for a short time so I use it. 50/17 (77") is too high and a major gear shift away from the 34/13. I race on a 12/23 so do not have this problem then as I only use the 50.
    I still recommend getting the correct mech. It does not cost much, is far safer and enables more gear options. As a Yorkshire man I do not often say go for the dearer option but here the cost of compromise could be far greater.
    My Fleet.
  • maddog 2
    maddog 2 Posts: 8,114
    I agree with the above but I run a slightly different setup to most. I run a 12-27 on a compact with a short cage mech and it's fine. However, I run the chain quite long, so big-big is okay (and I run it sometimes) but I never run small-small. I always shift back onto the bigger ring before then.

    As said, if you want it to be completely safe then a longer cage is necessary. However, if you never run small-small and your memory isn't shot, then a short cage will be okay.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • John.T
    John.T Posts: 3,698
    I run the same as you on 3 bikes Maddog. Also with no trouble at all. My position is that it is as far as you can safely push a short mech. As many on here do not have as much experience as we do it is bad form to recommend going further. If you know what you are doing and are prepared to live with the limitations then go for it. But if you had to ask then you are not yet in this catagory.
    My Fleet.

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