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  1. #1
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    Reputation: r0nin89's Avatar
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    Converting my 21 speed to a 7

    Hi all. I'm new to the whole mountain biking seen although I've always tinkered with BMX bikes. I'm a major 4wheels and decided it would be a good thing to pickup a mountain bike for those days I didnt feel like filling my tank to hit the fullsize trails. Plus since getting my license I've become alot less active so back on a bike i go.

    I bought an 02 or 03 or 04 Specialized Hardrock with no disc's off my dad who got it so it could sit in our basement for 3+ years. So now I'm in the process of making it mine. I want to convert it to a 7 speed for the simplicty and to remove one more factor of failure in the driveline. It has Truvativ X-Forge cranks on it which I am pretty happy with.

    Now my original thoughs were that I was going to pull the cranks, get a spacers and throw a bmx sprocket right on since the crank arms dont branch out to the sprockets on there now and seem like they just pinch it like a traditional bike. A friend of mine that works at a bikeshop with a few knowledgable guys said that not only would I need a specific sprocket bt also 2 chain guides to replace the de-railer to ensure my chain wont just flop off my sprocket.

    Anyone have any input or a write up on the precedure to change to single sprocket? I figure it will be alot like an SS conversion but just doing the front end of the driveline.

  2. #2
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    Reputation: oldskoolbiker's Avatar
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    Just remove your front derailleur and shifter. Remove your granny gear and big ring. Replace your big ring with a bash guard. And install a Jump-stop.

    http://www.gvtc.com/~ngear/

  3. #3
    local trails rider
    Reputation: perttime's Avatar
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    Quote Originally Posted by oldskoolbiker
    Just remove your front derailleur and shifter. Remove your granny gear and big ring. Replace your big ring with a bash guard. And install a Jump-stop.

    http://www.gvtc.com/~ngear/
    The rear deraileur usually has enough slack to allow the chain to jump off a single chain ring, unless you use some sort of a guide.

    A bash ring will keep the chain on, on the outside, and also protects the remaining chain ring. A Jump Stop, or something similar, takes care of the inside.

    A front deraileur, fixed in one position, can also work as a guide if you do not want to buy new parts.

  4. #4
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    Quote Originally Posted by perttime
    A front deraileur, fixed in one position, can also work as a guide if you do not want to buy new parts.
    Yeah - that's how I got my 7 speed (my new-old-pub-bike). The front der rusted from sand and crap.

  5. #5
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    Alright thanks guys! Will I have any trouble putting a BMX sprocket on there?

  6. #6
    local trails rider
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    I suspect a BMX chainring might not be compatibe with MTB cranks (there's a couple of different standards for MTB too).

    If you do not want to use your existing chainring you could get a single ring, for example by Blackspire. Just make sure you get the correct bolt pattern.

  7. #7
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    Damn alright. My cranks have a square tapered spindle I dont know if that makes a difference or if theres an adapter. Now removing the granny low sprocket doesnt effect spacing on the cranks?

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