chainring compatibility

Phekdra
Phekdra Posts: 137
edited May 2008 in Workshop
Hi all - I'm thinking of changing the compact chainrings on my bike to a standard double and using a wider range cassette. I've had a look at the drive side crank arm where it screws in to the rings (spider?) and it looks like the bolts are located just on the rim of the 34 ring. In order to fit a 39 ring I'd imagine the spider arms would have to be shorter or the 39 ring would have to have bolt holes on arms interior to the ring.

Hopefully all that makes some kind of sense! :) What I'm really asking is whether I can fit a double or compact to the same crank arm without having to replace the cranks.

Phekdra

Comments

  • meagain
    meagain Posts: 2,331
    If you can measure or "find" the BCD (bolt centre diameter) of the crank arm then you will be able to establish what rings will fit. Sorry if I'm telling you stuff you know, but the BCD is the diameter of the circle on which the centres of the holes to which the ring(s) sit.

    Edit : or perhaps it's bolt CIRCLE diameter - can never remember but the meaning is the same!
    d.j.
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  • Phekdra
    Phekdra Posts: 137
    meagain wrote:
    Sorry if I'm telling you stuff you know, but the BCD is the diameter of the circle on which the centres of the holes to which the ring(s) sit.

    No, I was entirely ignorant of the existence of BCD until this message - in fact I was just looking at some chainrings wondering what on earth BCD meant! Thanks very much, it all makes sense now! :)

    Phekdra
  • redddraggon
    redddraggon Posts: 10,862
    If you already have a compact you can get 53/39 rings with 110mm BCD to fit, but they won't be as stiff as the 130mm or 135mm BCD rings on "Standard Cranksets"

    However I'm sure why, you'd do it, do you already spin out on 50-11? If not I'd suggest swapping the 34 ring for a 36 or 38 and leaving the 50 in place. As you are on Shimano? I'd suggest changing the 34 for a 36 and fitting a 11-28 SRAM cassette. SJS Cycles have the Chainrings if you wanted to do 53-39 conversion though.

    53T chainring to fit on Compact

    Inner chainring
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  • fearby
    fearby Posts: 245
    TA do a ring to fit compact chainsets (Nerius) - presumably better quality than those listed above as the price is higher:

    http://www.dotbike.com/ProductsP2211.aspx?TRACK%3dDDI

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