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Sproket & front mech info & help please

wsamohtiwsamohti Posts: 3
edited December 2014 in Workshop
Hello all,

I'm new here so seeking to dip into your knowledge.

On my road bike I run a 105 group set. The rear sprocket is 11-28, were I live is hilly and I find at times I run out of gears, although I am improving !

I know a lot of people will say keep at it, try harder, loose weight etc, but I'm only at 48kg anyway !

I have recently swapped the rear sprocket for a sram 12 -32, which makes the steeper hills now significantly doable, but I get some chain rub on the from mech due to the chain line.
My technical question is this - If I swap the front mech to a sram that is designed for running the 12-32 will this stop this? are the widths of the plates on the front mech different dependant on the range of sprokets they are designed to be run with?
I don't want to do it to find it doesn't help. One day I might be able to swap back to the 11-28 :-)
Thanks in advance
i

Posts

  • deswellerdesweller Posts: 5,175
    I don't think you can run the SRAM front mechs with Shimano shifters (although I'm not 100% certain).

    You might be able to find lower gears by changing the front chainrings; what chainset do you have?
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  • Hi
    Thanks for your reply.
    I'm sure it's a compact, 50 -34 chain rings.
  • mattvmattv Posts: 992
    You have different problems here. The 32t cassette will not alter the chainline to create front mech rub. If it's definitely the front mech rubbing then something has been knocked or the mech is not set correctly. More likely is the rear mech not set. There is a screw into the back of the mech, on its own with no label. This is your "b tension" screw. The bigger cassette will be closer to the top jockey wheel, so you'll need to tighten this screw til there is around 5mm clearance (when in the granny ring front, easy gear rear). The noise you are getting is probably the cassette rubbing on the jockey wheel.
  • trailflowtrailflow Posts: 1,311
    Have you tried adjusting the low limit screw on the front derailleur?

    If you are running a short cage 105 rear derailleur (max capacity is designed for 28t) and a 32t cassette. Its probably likely you might need a longer chain aswell.

    If your chain is too short you risk wrapping the rear derailleur around the cassette and destroying everything.
  • StillGoingStillGoing Posts: 5,207
    Presumably you aren't cross chaining i.e. riding big/big? If you are, chain rub is inevitable unless you run SRAM which is designed to allow it. Having said that, you shouldn't do it for any length of time.

    On your gearing; I'm surprised someone so light needs a 34/32 option for hills. I'd love to be a few kgs behind you when it comes to hills. The gaps between the gears on a 11/32 cassette aren't nice either. I'm no demon at climbing, but I found effort far exceeded forwards momentum with an 11/32 cassette and opted to go with a 12/28 and stick at it. Pace yourself to what you can do and not what anyone else is doing, and you should be able to make it up most things.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
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