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Thread: Bmx

  1. #1
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    Apr 2013


    What is the best way to change a 27 speed into a single speed for dirt jumping? As in what parts to buy etc. I have jumped it enough that I know it's good for jumping, but the chain and derailleur rattle are annoying.

  2. #2
    Bro is offline
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    Quote Originally Posted by Jmartin98 View Post
    What is the best way to change a 27 speed into a single speed for dirt jumping?
    Take the shifty bits off. That's generally the best way for converting to singlespeed.
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  3. #3
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    Oct 2007
    It's really as straightforward as it seems. As Bro said - take off all the "shifty bits". You'll need a few things to put back on...
    - Brake levers - if they're integrated with shifters. These are cheap and easy find - check the interwebs
    - Spacers for the cassette. Once you take off the 9-speed cassette, you'll need something to fill that space. I've used the Forte (Performance Bike) conversion kit - spacers, chain tensioner and several (heavy) cogs. I'm sure a search of the interwebs will yield another source for the spacers.
    - Single speed chainring bolts - yours are too long.
    - A half-link... maybe

    - Remove both derailleurs, the shifters, cassette, etc. Use the middle chainring (you'll have to pull the crank to get the small ring off).
    - Divide that chainring by 2 - that's the cog for the rear, e.g. 32:16.
    - Use the spacers to locate the 16-tooth cog so it's in line with the chainring. This may take a few attempts, e.g. swapping spacers around, etc.
    - Cross your fingers. You're hoping for the "magic gear" - that gear that lets you run that 32:16 without a chain tensioner. There's no real downside to a chain tensioner. Single speeds are just cooler without them.
    - If you didn't stumble on the magic gear, all's not lost. There are two ways to get there (without track drop-outs that is)...
    --- Swap that 32 for a 34 and use a 17 in the back, or another combination of gears
    --- Use a halflink. Do a Google Image search on that if you're not familiar - very cool solution.



    Side note: If you're not good with a chain tool (breaker), you will be by the time you've built a single speed - especially if you're on a quest for that magic gear. Have fun - it's a cool project.

    I usually convert my old bikes to single speeds when they're replaced. I've found the magic gear on each that I've tried. When you "rerail" the chain, it should have a bit of droop across the top - it shouldn't be overly tight. Here's another example - note the slight droop across the top. This bike has a few thousand miles on it in this configuration:
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