Using a 'traditional' double front mech with compact cranks?

garethrl
garethrl Posts: 53
edited April 2010 in Workshop
I have a compact 50/34 crankset to go onto my roadie to replace a 53/39 that's currently on there. I was just wondering if I can still use the Dura Ace 7700 front mech that I have on, or do I need to buy one of these new 'compact compatible' front mechs? I know that Shimano claim that the 7700 one is for 15T ring difference or less and that the new 7900 and Ultegra 6700 ones are the ones to use with a 16T difference compact setup - but how much of that is marketing vs engineering??

I've not had two examples together to compare them closely, but how much do the cages differ in terms of length and curvature? My mech is a braze-on type so could be lowered sufficiently, I would expect. On top of that, I could shim the top of the clamping section a bit to rotate the cage anti-clockwise and match the smaller rings a bit.

Has anyone tried this, with any success? Apologies if it's been covered before, I tried a quick search but didn't see the answer.

Cheers, Gareth.

Comments

  • softlad
    softlad Posts: 3,513
    standard front mech will work fine - you might need to adjust the height a bit, but that's all...
  • Wappygixer
    Wappygixer Posts: 1,396
    I wont work very well at all.
    That one tooth difference doesn't sound like much but it is there for a reason.
    The 6700 Ultegra ones will work with both standard and compact.due to the cage design.
  • softlad
    softlad Posts: 3,513
    so, one says it will - and one says it won't. I suppose theonly option is to try it yourself.

    All I can add is that I have run an old 'pre-compact' ultegra front mech on a compact setup and it did the job....
  • Ben6899
    Ben6899 Posts: 9,686
    I think there have been threads on here in the past where people have had trouble using the 'standard' mech with 'compact' rings... well, here or BikeForums.net.

    But I cannot offer any personal experience.
    Ben

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  • Smokin Joe
    Smokin Joe Posts: 2,706
    It will work perfectly.

    If anyone has reported problems using this setup it is because they have made a feck-up of setting it up.
  • Mister W
    Mister W Posts: 791
    The issue is likely to be with the chain rattling on the mech when it's on the small ring because of the larger size difference between the two rings. Shimano say that the maximum difference is 15T but they are generally quite generous on their specifications so I wouldn't be surprised if it does work with a 16T difference. Try it and see.

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