105 chainset query

KMC1993
KMC1993 Posts: 101
edited September 2015 in Workshop
Hi, Im just wondering whether I can stick a compact inner ring on to my standard chainset or would the drop from 53 to 34 be too big and cause crappy shifting?
Having moved somewhere a bit more bumpy I'm finding my aggressive gear choices to be a little bit idiotic :?

Comments

  • keef66
    keef66 Posts: 13,123
    Which 105 are we talking about? New 11 speed 5800 stuff, or older 10 speed?

    If the former, the standard BCD of the chainset means you can fit more or less whatever size rings take your fancy. If it's 5700 or earlier, your 53t chainset will have a BCD of 130mm and you'd not be able to fit a 34t

    You'll also need to consider whether or not your rear mech has the total capacity to cope with the difference in chainrings + cassette range. It needs to work in both big-big and small-small combos.

    I also think the drop from 53 to 34 would be pretty hard to live with on a daily basis.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    Might be worth considering semi-compact (36t) or a bigger cassette. I actually ride a 53/39 on a couple of bikes but match this with a 13/28t 9 speed cassette which works well for me.
  • KMC1993
    KMC1993 Posts: 101
    Its the last 10 speed version, may just have to find a compact chainset and swap them over then.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    mmm, a 130BCD gives a 38t as the smallest chainring so the semi compact options looks to be out. Hence, cassette or compact looks to be the way forward.
  • KMC1993
    KMC1993 Posts: 101
    At the moment I have a 11-25 10 speed cassette on, would a swap to 11-28 give a real difference?
  • fallenagain
    fallenagain Posts: 25
    Moving from a 25 to a 28 rear will lower your gearing by about (1-(25/28) = 11%.
    Moving from a 39 to a 34 front will lower your gearing by about (1-(34/39) = 13%.

    Take your pick.
  • KMC1993
    KMC1993 Posts: 101
    I dont know why but i thought the front would have a much larger impact than that. But in that case a new cassette seems the better option and the cheaper one, just got to check whether my rear mech will take a 28 tooth now.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    Most of them will take a 28, even if the spec says that's at the limit. You will probably need to wind the B Stop down to a minimum and check the chain length after fitting the cassette but a new 11-28 cassette can be had for £20 if you shop around. Might be worth a punt to see how you get on.

    This is a good gear site, allows you to compare options.

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