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Chainring ratios – advice

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  • August 10, 2016 at 10:53 am #26118
    barrydocks

    Hi there,

    A bit of advice from the people that know these things:

    I currently have a 9speed Tiagra 4503 triple on the front with 50-39-30

    What is the smallest ring I can put on the granny gear?

    Based on the answer above, what woul the middle and outer rings then need to be?

    Thanks

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  • August 12, 2016 at 11:28 pm #876495
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    SilverBugle

    I have got the Sora triple

    I have got the Sora triple (FC-3503) not Tiagra, but they both have an inner BCD of 74.  Technically you can go as low as 24 for your inner.  On my Sora i have replaced the stock 30 with a 26 and without having to make any adjustment to the position of the braze on front derailleur (Sora triple) it still shifts perfectly.  Theoretically this makes the tooth difference larger than the stated capacity of the mechs but in reality it is fine.  This means you can keep your 50-39 but improve the your range at the bottom end.  Spa have a range of 74 BCD inners from TA, Stronglight and Spa.  The Stronglight Zicral ones look the best value.

    August 11, 2016 at 12:09 pm #876493
    0
    Simon E

    I also have FC-4503, the

    Good to know that 28T will work. I also have FC-4503, the inner ring BCD is 74mm.

    Whether it shifts accurately probably depends on the front mech, including whether it can be positioned low enough on the seat tube to shift to/from a chainring significantly smaller than 30T.

    You may like to investigate a super-compact or touring chainset like those available from Spa Cycles (e.g. this one & this one).

    August 11, 2016 at 9:43 am #876491
    0
    BlindFreddy

    On 105, a 28 granny

    On 105, a 28 granny definitely works. A 24 granny works if you make a whole shift to the middle ring upper trim position. Suspect 26 works ok.

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