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  • Groupset dying…where to next?!
  • donslow
    Free Member

    The groupset on my trusty BMC Aplenchallenge hybrid/gravel/commuter bike is on its way out so will need renewing in the new future

    Currently have Shimano Sora 2×9
    50-34 up front
    11-32 in the rear

    I’m looking at possibly going to a single chainring up front as I rarely use the smaller chainring…But what to go for?!

    Happy to keep the 9 speed cassette as is but wondering what chainring would give me a decent spread of gears for (give or take) 80% flat-ish (mostly city) commuting
    20% hills and climbs

    I only use the smaller chainring on one hill (12% incline for around 0.4 mile) and only go halfway (at most) up (or is it down?!) on the cassette when I do

    Something that will let me go quick on the flats and handle climbs without grinding up, prefer to keep the crank arms if possible so something compatible with those would be ideal

    Suggestions please…many thanks

    donslow
    Free Member

    Crank arms are the same as these

    B4-DE578-C-592-C-4-C9-B-8072-87407-B36-A347

    dyna-ti
    Full Member

    Well this is bargains season, so scan through the different sellers/shops/outlets and whatever is the best price/biggest saving go with that. Even if its mix n match.

    donslow
    Free Member

    Ha ha I guess you’d call that good timing

    Mixing and matching is fine as long as it works

    Just need advice as to what size chainring would be a good option as a single ring given my requirements and which would be compatible with my crank arms

    irc
    Full Member

    Stick your current gears in this calculator. It will give you a list of your current gears in your choice of output. I like gear inches.

    Then try different sizes of single front rings with different rear cassettes.

    https://www.sheldonbrown.com/gear-calc.html

    My approach is to start with what is the highest low gear that is acceptable. Then compromise on top end.

    For what it’s worth around town my 1×9 bike has a 38t front and either 11-32 or 1134 at the back. Can’t remember offhand. Gets my up the hills I need to and spins out around 23/34mph. I’mm more of a spinner than most people. Starting of with a 42T ring in the gear calc might work. Or 44.

    PS – The starting point for chainrings fitting the crank arms is the BCD

    https://www.wolftoothcomponents.com/pages/how-to-measure-bolt-circle-diameter-bcd

    So most chainrings with a matching BCD should fit your crank arms though sometimes a few minutes with a file is needed.

    timba
    Free Member

    I think that the Sora 9s is a 4-arm 110BCD (check this-I haven’t 🙂 )
    Size of the chainring is going to have to be down to you using a gear table as suggested by irc^^
    If you use an outer Shimano chainring alone then they are expensive. The inner is cheaper but won’t give you the higher gears
    I’d buy a single chainset from somewhere like Spa Cycles https://www.spacycles.co.uk/m8b0s109p0/Drivetrain/Chainsets and a BB to give you the correct chainline

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