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Thread: Higer top gear

  1. #1
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    Higer top gear

    hi,

    i've got an 18 speed mountain bike which doesn't have a high enough top gear. i can't get enough speed out of the bike before the gearing reaches its limit.

    how can i change this? would a 21 speed bike be better or is it simply the size of the front cog which counts.

    if i was to buy another gear set or bike what sort of measurement should i look at which tells me the gearing ratio of the any given bike?

    thanks
    James

  2. #2
    Gone, but not forgotten Sheldon Brown's Avatar
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    Quote Originally Posted by jiminwatford
    hi,

    i've got an 18 speed mountain bike which doesn't have a high enough top gear. i can't get enough speed out of the bike before the gearing reaches its limit.

    how can i change this? would a 21 speed bike be better or is it simply the size of the front cog which counts.

    if i was to buy another gear set or bike what sort of measurement should i look at which tells me the gearing ratio of the any given bike?
    The number of gears has nothing to do with it, it's the sizes of the biggest front and smallest rear sprocket that determine how high the highest gear is.

    It's usually cheaper and easier to change the back than the front. Your bike will need an old-style thread-on freewheel.

    See: http://sheldonbrown.com/freewheels

    and: http://sheldonbrown.com/gears

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  3. #3
    cycles per second Gonzo Bob's Avatar
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    If your rear hub has a Uniglide freehub, 12T is as small as you can go and you can get a 12T cog at Loose Screws http://www.thethirdhand.com/index.cg...id=53386728737 This is what I did on my old MTB (46/12 is big enough for me). You could also swap the Uniglide freehub for a Hyperglide freehub and get a 7-speed Hyperglide cassette that starts with an 11T. This is what I did on my old touring bike.

    If it's a freewheel, the only way to go to a smaller than a 13T cog is with a 7-speed - Shimano makes 11-28 and 11-34 7-speed freewheels. Of course, if your rear shifter is indexed for 6, you will need to switch to friction. If it has no friction mode, you will need a new rear shifter for 7-speed.

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