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Converting 21 speed to singlespeed

amack23amack23 Posts: 46
edited April 2013 in MTB workshop & tech
Hi all, new member here. i have an old 21 speed from the late 90's, was a half decent bike at the time. Now looking to give a make over and convert to singlespeed. What parts exactly would i need. I'm replacing the bottom bracket and cranks anyway so is it best to go with a singlespeed crankset and a sprocket and spacers on the back? and what chain?
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  • amack23amack23 Posts: 46
    It's a cassette
  • cooldadcooldad Posts: 32,599
    Singlespeed conversion kit, chain tensioner and single speed chain. And a chain guide for the front, or just use the mech.
    Unless it has horizontal drop outs.
    If you are sure it is a freehub and not a freewheel.
    I don't do smileys.

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  • amack23amack23 Posts: 46
    is a chain guide necessary if using a dedicated singlespeed chainring? I wont be using it offroad
  • cyclecliniccycleclinic Posts: 6,865
    Easy. Use a tensioner the push up kind and whatever gear ratio works for you a 32:16 or 1:2 ratio work well for most.
    To do this without a tensioner requires abit more cunning. First of all you need to know that chain wrap will change with the size of the sprockets you use. Changing the number of teeth on the front or rear sporcket will add or takeaway 1/4" from the length of the chain. So adding 2 teeth to the front a an 2 teeth to the rear sprocket will add 1" total to the chain length required. Using this you can determine what sprockets/ chins ring combo is needed to give correct chain tension without a tensioner. Frist wrap your chain around the middle chainring and one of your rear sprocket no going through the mech. Then find the rear sprocket that gives you the correct or near correct chain length. If you are 1/4" from joining the chain then adding one tooth or taking one away by changing a sprocket will give you the correct chain length. Then you can work out which sprockets you need to give you a 1:2 ratio.

    For my bikes which were SS a 1:2 ratio was achieved by 36:18T drive. A 34:16T drive could be used as well by taking 1" from the chain. I hope that's clear and this works very well for a road use and off road use.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Easy. Use a tensioner the push up kind and whatever gear ratio works for you a 32:16 or 1:2 ratio work well for most.
    To do this without a tensioner requires abit more cunning. First of all you need to know that chain wrap will change with the size of the sprockets you use. Changing the number of teeth on the front or rear sporcket will add or takeaway 1/4" from the length of the chain. So adding 2 teeth to the front a an 2 teeth to the rear sprocket will add 1" total to the chain length required. Using this you can determine what sprockets/ chins ring combo is needed to give correct chain tension without a tensioner. Frist wrap your chain around the middle chainring and one of your rear sprocket no going through the mech. Then find the rear sprocket that gives you the correct or near correct chain length. If you are 1/4" from joining the chain then adding one tooth or taking one away by changing a sprocket will give you the correct chain length. Then you can work out which sprockets you need to give you a 1:2 ratio.

    For my bikes which were SS a 1:2 ratio was achieved by 36:18T drive. A 34:16T drive could be used as well by taking 1" from the chain. I hope that's clear and this works very well for a road use and off road use.

    Rarely works well in my experience. As soon as the chain wears a bit and lengthens it goes out of whack.
  • amack23amack23 Posts: 46
    So a tensioner and no chain guide. Is a 1/8 chain preferable to 3/32?
  • amack23 wrote:
    Hi all, new member here. i have an old 21 speed from the late 90's, was a half decent bike at the time. Now looking to give a make over and convert to singlespeed. What parts exactly would i need. I'm replacing the bottom bracket and cranks anyway so is it best to go with a singlespeed crankset and a sprocket and spacers on the back? and what chain?
    Get it done by a bike dealer or get a conversion kit or if you are skint just shorten the chain on the sprocket you feel best in, up to you.
    And I didn't want to sound rude asking if you are skint!! :(
    road: carrera tdf ltd 2012
    xc: gt avalance 1.0 2008

    love cycling :)
  • amack23amack23 Posts: 46
    Hi, no not really skint :D , have a road bike and a hardtail and fancied giving an old dog in the corner of garage a new lease of life. I'd actually prefer to do it myself, have a garage with workstand a few tools a haynes manual and a willingness to learn. Dont really want to go down the ghetto route. I stripped the threads on one of the cranks taking it off, though the bottom bracket looks ok, mite actually keep it on there. Are all square taper cranks universal fitting?
  • The RookieThe Rookie Posts: 27,757
    Yes, only one square taper standard....

    Haynes isn't that good, much better to check on parktools website or ask here!

    A friend has built an SS rigid out of an old frame, uses a push up tensioner, and SS convertion for the freehub, even used an old middle ring up front for a while.
  • amack23amack23 Posts: 46
    Yeah, coming to realise that. Didn't say anything about taking the mushroom shaped end bit off the crank puller b4 using it ....... ....there goes the threads :oops:
  • The RookieThe Rookie Posts: 27,757
    Older crank pullers don't have it, only those for ISIS/Powerspline/Octalink.....to be honest, it's easy to tell when it's 'not right'.
  • crakercraker Posts: 1,739
    Get it done by a bike dealer or get a conversion kit or if you are skint just shorten the chain on the sprocket you feel best in, up to you.

    I find that using gears and chains from a derailleur equipped bikes means that the chain wants to jump off the gears - after all the gears all have ramps to enable smooth shifting and the chain is flexible. you want to get your chainline pretty straight and use single speed specific cogs and chainrings if possible - actually i've got away with a 7 speed chain, the small chainring from a double chainset and a single speed specific gear at the back; it's been pretty reliable so far.
  • amack23amack23 Posts: 46
    So it doesn't matter what size chainrings and cogs i go for if I'm using a tensioner. 32/16, 36/18, 44/22 etc are all the same gear?
  • supersonicsupersonic Posts: 82,708 Lives Here
    Yep. Smaller front chainring gives more ground clearance. Larger is heavier but wears down less quick.
  • amack23amack23 Posts: 46
    Just looking at the price of some those singlespeed cranksets and all seem to be 44t - 48t, be better to buy this (http://www.chainreactioncycles.com/Mode ... elID=46021) and fit a single chainring?
  • supersonicsupersonic Posts: 82,708 Lives Here
    Is a good option, as you can sell the chainrings for good money.
  • cyclecliniccycleclinic Posts: 6,865
    Funny supersonic how I managed to about 2 years riding week in week out like that. Yes I do say the chain has to be changed fairly regularly but if you use a 1/8" then chain life is resonable and it last for more than a few rides. A tesnioner is simpler but I abondened them as I tried several like the BB mounted push up kind and found that more of a faff. The whole point of single speed is to remove jockey wheels and keep it simple. Running with a tensioner means you have to know what you are doing and you do get silent drive.

    I also used a ramped chainring and in about 6 years of riding SS this way I never had a chain jump off and was with riding hard of uneven ground and racing, wales cannock e.t.c. you have to use a single speed specific rear sprocket the extra teeth length helps there. TA chainrings seem to have enough teeth depth even though they are ramped to prevent the chain coming off.

    It would appear I have not had the bad experience other have had with this setup I do not believe it is luck as I had it two different bikes.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • Chunkers1980Chunkers1980 Posts: 8,035
    I'd hope your chain lasts more than a few rides.
  • amack23amack23 Posts: 46
    Me too......... Cranks, chainring, cog and 1/8 chain ordered..... Come on Mr Postie
  • amack23amack23 Posts: 46
    Ok parts came. I'm wondering, will I have any issues running a 1/8 chainring and chain with a 3/32 rear sprocket?
  • crakercraker Posts: 1,739
    No but you'll have to use a chain suitable for the chainring.
  • amack23amack23 Posts: 46
    Yeah, have it fitted now, using a 1/8 half link chain. I'm using a superstar push down tensioner, is there a way to make it push up?
  • The RookieThe Rookie Posts: 27,757
    Is it sprung loaded or bolted up?

    Either way it can be run push up, use a cable tie to pull it up if it's sprung, or just bolt it up if it's not.
  • amack23amack23 Posts: 46
    It's a spring. Do I take the spring out or does it matter?
  • The RookieThe Rookie Posts: 27,757
    Leave it in if you can (from a resale point of view), having said that if you got a half link chain your chain should be close enough in size that pushup or pushdown should make very very little difference.
  • amack23amack23 Posts: 46
    Took the spring out but sits very loose on the frame, guess I'll leave it in. Even with the half link chain It's still slack and can't take any more links out as it's too short then. Actually tried an ordinary 1/8 chain first and it was slipping badly under heavy load. The half link chain seems fine so far but has only slightly more chain wrap so probably best to push the tensioner up. Can a standard and a half link chain be mixed, or is that a bad idea? Can't seem to upload a pic
  • amack23amack23 Posts: 46
    2w24xv7.jpg

    This is it with the half link chain
  • amack23amack23 Posts: 46
    14l3m6p.jpg

    This is with standard chain. ( was slipping with this on it )
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