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Thread: Bmx

  1. #1
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    Bmx

    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
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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.
    I've made some bad decisions like taking the gears off my bike. So here's the warning: Do not as I say, nor as I do.

  3. #3
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    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.

    Before:


    After:


    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:
    Mountain bikers who don't road ride are usually slow.
    Roadies who don't mountain bike are usually d***s.

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