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11-32 or 11-34 cassette help

dartmoorcyclistdartmoorcyclist Posts: 33
edited February 2014 in Workshop
Hi,

Wanting to tour on my road bike, carrying a small load. Currently has 50-34 chain set and 12-28 cassette which is already tough enough on Dartmoor hills. Hopefully I have uploaded an attachment with rest of the spec.

Could anyone tell me whether there is an option of a cassette only change, or cassette and rear mech if necessary, I'll need a bit more help on the hills and up to 32 or 34 should help I think.

Thanks.

Posts

  • mr_evilmr_evil Posts: 234
    The short cage (SS) version of that rear mech has a specified max of 30t for the rear sprocket, while the medium cage (GS) is 32t. Even with the short cage, 34 may work if you adjust the b-screw all the way out (Shimano are very conservative with their specs). However, you will exceed the wrap capacity of a short cage (only 33t), but a medium cage will be ok (39t capacity, which is exactly enough for 50/34 chainrings and a 34-11 cassette).

    You may also have to change the chain, depending on how short it was cut when installed.
  • Thanks Mr Evil, do you know if any Shimano cassette will do? Struggling to fid a road shimano cassette at 11 or 12 to 34, perhaps they don't exist? Will this one do - if the RD is a long enough cage: Shimano HG81 SLX 10 Speed Cassette Thanks.
  • From other threads it looks like this cassette will work if I have GS RD and get a new chain:
    SRAM PG1050 10 Speed MTB Cassette
    Thanks Mr Evil.
  • I have more or less the same set up and use the SRAM PG-1050 10 Speed Cassette which is marketed as a road cassette.

    Whether it will work for you depends a little on the construction and layout of the rear deraileur hanger and the rear end of the frame.
  • Thanks freezing, good to know. Can you say anymore about the construction / layout? This will be more work than I have done on a bike before. If I try it out and find I need a new RD too, that's okay, but if you can give me more pointers then useful please.
  • Thanks freezing, good to know. Can you say anymore about the construction / layout? This will be more work than I have done on a bike before. If I try it out and find I need a new RD too, that's okay, but if you can give me more pointers then useful please.

    Unfortunately I do not know enough about the geometry of different rear triangle and derailleur hanger arrangements to make a quantifiable statement.
    My frame is a Ribble Gran Fondo and it works, for others I know with different frames, for some it works for others it does not. I do not have details on these, just odd snippets picked up.
    I would try it and see. Thats what I did, at worst I would just need a new rear deraileur which in my case was not needed.
    May try to post some pics.
  • thanks!
  • CPeacheyCPeachey Posts: 1,057
    I have a 105 rear 10sp changer working with a 11-34t cassette. Frame is a 1960's tourer. When I first tried it the jockey wheel "scrubbed" the 34t spocket but DID engage. Re-fitted it a few weeks later and it now clims onto the 34t ok, without horible noises so it is worth trying.
  • If the rear derrailer does cause issues it isn't expensive to get a long cage 9speed mtb mech which will work flawlessly
  • Monty DogMonty Dog Posts: 20,614
    I have a Specialized bike in for service which has been fitted with a 12-34 cassette and 105 GS rear mech - there's insufficient clearance for the top jockey wheel and doesn't run smoothly. You'll need to fit a MTB rear mech if you want to run a bigger sprocket than a 32. The mech hanger on most modern frames isn't long enough to give the clearances.
    Make mine an Italian, with Campagnolo on the side..
  • Monty Dog wrote:
    I have a Specialized bike in for service which has been fitted with a 12-34 cassette and 105 GS rear mech - there's insufficient clearance for the top jockey wheel and doesn't run smoothly. You'll need to fit a MTB rear mech if you want to run a bigger sprocket than a 32. The mech hanger on most modern frames isn't long enough to give the clearances.

    Have you tried a longer B-screw??? Just out of curiosity,
  • Monty DogMonty Dog Posts: 20,614
    Have you tried a longer B-screw??? Just out of curiosity,

    Pushed the mech forward by hand and it doesn't make any difference - it's simply down to the geometry of the mech and the upper jockey wheel being too close to the wheel. The only solution would be to fit a longer rear mech hanger which simply doesn't exist.
    Make mine an Italian, with Campagnolo on the side..
  • CPeacheyCPeachey Posts: 1,057
    Works ok on my bike but could this be because the hole in the hanger is a little further from the wheel axle? I have not measured it yet. It does seem to be down to the individual frame.

    Update..
    On the old frame with horizontal dropouts the changer bolt centre is about 3mm further from the axle compared to the tandem which has vertical dropouts. This would give 3mm more clearance between the big cog and top jockey wheel.
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