Lowering 105 gearing

whobiggs
whobiggs Posts: 23
edited May 2012 in Workshop
I've been trying to lower the gearing for someone on a bike with 105 triple. I've fitted a 12-36 instead of the 11-28 original cassette and tried a 10 speed Shimano rear mech (Dyna sys) which is not compatible, also tried a Deore 9 speed which was supposed to work but that doesn't either. Can anybody help me with this problem?

Comments

  • rpd_steve
    rpd_steve Posts: 361
    I cant see that a 32T cassette shoud ever be required even when an amiter is climbing an alp.

    What chain rings are on the bike? I would be looking there. You will get some poor shift quality with a cassette that big and will struggle to get a road mech with a long enough cage.

    My guess is that is on a 53/39 crank and you need 50/34 or a tripple with 12-27 cassette.

    Why are gears that amall needed? Not trying to be silly or saying MTFU but that is amazingly low...
  • mister p
    mister p Posts: 405
    To run a 36T sprocket on a 10 speed road bike you need to use a Shadow 9 speed MTB mech. Something like an SLX RD-M662 would do the job.
  • whobiggs
    whobiggs Posts: 23
    It is for a pensioner on her light touring/audax bike. I can't find any chainrings lower than 30t without changing the crankset. I've got a 10 sp Deore RDM593SGS which doesn't pull enough cable and a 9sp RDM592SGS which is almost there but not quite indexing properly.
  • mister p
    mister p Posts: 405
    The 592 is compatible with the set up you have so the mech shouldn't be the issue. I assume you have done all the usual stuff like check the mech hanger is straight, cable is moving freely, cable is clamped to mech correctly, etc?
  • whobiggs
    whobiggs Posts: 23
    mister p wrote:
    The 592 is compatible with the set up you have so the mech shouldn't be the issue. I assume you have done all the usual stuff like check the mech hanger is straight, cable is moving freely, cable is clamped to mech correctly, etc?

    Yes I've done all that. Maybe I should go and have another go. Thanks
  • desweller
    desweller Posts: 5,175
    Don't forget that you'll need to adjust the B-screw so the derailleur maintains the correct gap from the biggest sprocket.
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  • peterbayliss
    peterbayliss Posts: 16
    whobiggs wrote:
    I can't find any chainrings lower than 30t without changing the crankset.

    SPA cycles sell chain rings that will fit for example http://www.spacycles.co.uk/products.php ... b0s149p245 however the M592 SGS rear mech should work with the 12-36 cassette.
  • Barbarossa
    Barbarossa Posts: 248
    I've just fitted an 11-32 casette to my Ultegra equipped bike. Used a Deore T661 9sp. mech. Works fine.
  • whobiggs
    whobiggs Posts: 23
    SPA cycles sell chain rings that will fit for example http://www.spacycles.co.uk/products.php ... b0s149p245 however the M592 SGS rear mech should work with the 12-36 cassette.[/quote]

    I should have contacted them sooner. I have now fitted a Tiagra rear mech and 12-30 cassette with 28-38-48 stronglight rings from them. Brilliant advice and great service. My lady friend is extremely happy with the gearing now, she said it makes all the difference. She is now off to tackle Bealach na ba. Thanks to everyone for their help. :D

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