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Convert an old MTB to a Single Speed...?

Discussion in 'Bicycle Mechanics' started by StuInTokyo, Nov 11, 2011.

  1. StuInTokyo

    StuInTokyo Maximum Pace

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    As I sit here on a cool rainy night, my thought have wandered......

    I'm sure it is possible, the biggest problem I foresee is chain tension.

    I have my dear old 1988 Cannondale SM500 in pieces, I will attempt a fix on the two cracks in the top of the seat tube sometime in the future, but I was toying with the idea of making this old frame into a single speed or even a fixie (I can hear Tim S cheering already!) Why not, this bike started out life as a MTB, did a lot of that, then a touring bike, a city bike here in Tokyo, I put drops on it and tried to make it a road bike (big fail) and lastly it was a trailer tugging workhorse, heck I think the only duty it has not done is a single speed :D :rolleyes:

    As usual I want to do this on the cheap, most any problem can be solved by throwing money at it, but where is the fun in that? ;)

    The crank has three rings, a granny gear, a 38T and a 48T, I'm thinking of ditching two of those rings and then just putting a single sprocket on the rear. To do that I will try to use the freewheel hub that is on there with a spacer on either side of the single sprocket locked down by the lock ring that would normally lock down the cassette. Dunno if that would work, but I have a lathe and some delrin plastic (Polyoxymethylene) kicking around that I think I could work on my lathe to make the spacers...?

    With 26" rims and 175mm cranks, what kind of gearing should I look at?

    About the chain tension, what to do about that? I guess I might get lucky, but....? Half link?

    It is just a thought experiment at the moment, but who knows :D

    Comments welcome :eek:
     
  2. Phil

    Phil Maximum Pace

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    Re: chain tension, a chain tensioner will do the trick I think. Not sure if that falls under the throwing-money-at-a-problem category though...

    If you're removing the FD, by the way, it might be an idea to have a chainring guard on the outside and chain guard on the inside, to keep the chain from jumping off. This is what I did when I converted my Aquila to a single chainring up front (but still geared at the back). Not sure if this is really necessary, especially for a single speed, but no doubt the SS/fixie gurus will weigh in soon to confirm one way or another.
     
  3. StuInTokyo

    StuInTokyo Maximum Pace

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    Yeah a tensioner would work well, but I'd really like to have just a chain, but if that does not work then a tensioner would be the fix.

    Thanks!
     
  4. FarEast

    FarEast Maximum Pace Post Of The Week

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    Just try setting the chain first and then messing with cassette rings to get the right tention. I did this with the Pinarello and it worked out fine. You could always try using a half link as well.

    You are not doing anything new so there is plenty of info out there on the internet regarding single speed MTB setups
     
  5. GSAstuto

    GSAstuto Maximum Pace

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    This is how 'The Italians Do It' (Breaking Away). Play around with the gear combos and you'll find one magic combination that gives you decent chain tension with or without halflink. I rode my Panasonic (RIP) muletto years this way - including the locktighted cog cross threaded onto an old Araya 5speed hub.

    If you are going to use a freewheel cog and not a fixed cog, the tension is not so critical.

    If you wanna go 'luxe' then I can build you a 26" fixed wheel with ENO eccentric hub, proper spacing, etc. But the wheel would be worth more than the bike - so not advised.

     
  6. Deej

    Deej Maximum Pace 3rd TCC KOM 2012

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    Hi Stu. Sounds like a fun project! As you may know, I've occasionally used this site to blather on about The Bomber, my single-speed MTB.

    [​IMG]

    It's a mid-90s steel KHS. I slapped on some drop bars (sounds like that didn't work for you) and swapped out the old triple-cog drivetrain in exchange for a 44-tooth chainring up front and a 15-toother in back. I also added a tensioner.

    I can tell you in all sincerity that having this bike has been pure awesomeness. I can blast through the city, jam on dirt roads, steamroll across grass fields and take on the roadies on the Onekan.

    I have really enjoyed the single-speed aspect of the bike. It's simple and forces me to work a little harder on climbs (and adds a certain badass factor when drag-racing along the Onekan).

    Look forward to hearing how this project progresses!

    Deej
     
  7. patrick.yodar

    patrick.yodar Speeding Up

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    I've got a 26" rear wheel and a few chain rings lying around. I've also got a rear cassette with all loose cogs and some spacers if you're interested. i tried half links for a few days but found them too stretchy. stick with whole links if you can.
     
  8. ProRaceMechanic

    ProRaceMechanic Maximum Pace

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    Just an Idea

    You may be able to fit 700c wheels in the frame, no brakes though so has to be fixed.
    Then adjust the rake with one of GS Astutos Carbon forks.... Theres your front brake\
    ...Ahhh, its 1 inch, dont know if he makes those
     
  9. StuInTokyo

    StuInTokyo Maximum Pace

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    I might do the tensioner, just to be able to get the gear combo I want, but I think I'll be sticking with the freewheel for now. :D

    Very cool, thanks for that!
    What tensioner did you buy? I'm curious about that.

    Thanks for the info, maybe if I need an odd gear I don't have, I'll take you up on the offer! :)

    Got to have me some brakes! ;)
     
  10. StuInTokyo

    StuInTokyo Maximum Pace

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    While Timdesuyo was working on his wheel, I decided to turn the spacer for the Cannondale and see what the gear sets would look like....

    [​IMG]

    [​IMG]

    [​IMG]

    That is a 48/21 combo, I ran the 48/19 combo and it was too loose.

    I think that would be a good all round gear to get started with, but I don't know, what do you all run on your single speed set ups?

    Cheers!
     
  11. kiwisimon

    kiwisimon Maximum Pace

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    Stu, just use an old deraillier with the limit screws screwed down as a tensioner.
     
  12. StuInTokyo

    StuInTokyo Maximum Pace

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    Yep, thinking the same thing, but it kind of looks ugly, might just give it a go, once I fix the crack frame first..... :rolleyes:

    I found this on Wiggle.....

    View attachment 924

    around 3500 yen
     
  13. kiwisimon

    kiwisimon Maximum Pace

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    Lipstick on a pig!
     
  14. StuInTokyo

    StuInTokyo Maximum Pace

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    Gee, ya think :)

    I just might build one myself from some old parts :nosweat:
     
  15. kiwisimon

    kiwisimon Maximum Pace

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    Stu said":rolleyes:I just might build one myself from some old parts "

    Thatta boy!
     
  16. GSAstuto

    GSAstuto Maximum Pace

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    I hate those tension thingies - if you are riding fixed gear they are worthless and will just break. If you are riding freewheel, then 9 times out of 10 not needed cause you find a workable gear combo and a little slack in the chain won't be noticed.
     
  17. FarEast

    FarEast Maximum Pace Post Of The Week

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    :rolleyes: What he said..... no point in adding anything when you have sooooooooooo many gear ratios to play around with to get the chain taught.
     
  18. Deej

    Deej Maximum Pace 3rd TCC KOM 2012

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    Sure thing. The tensioner is made by Gusset. It appears to be selling for 2,930 yen online.
    [​IMG]
     
  19. StuInTokyo

    StuInTokyo Maximum Pace

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    I figured you'd like that :D

    Well I have a 17T 19T and 21T, none of them I can get the tension I want..... Plan "B"

    Thanks for that, very nice looking bit there, reasonable price too, but I built my own......

    [​IMG]

    [​IMG]

    [​IMG]

    It seems to work :)

    The thick block aluminum bit is does not rotate, it is that size to accommodate for the length of the bolt from the donated old derailer. The arm part with the idler wheel on it is spring loaded and provides tension. Might tweak it a bit more, but for now the idea seems to work, so I'll look at fixing the cracked frame.

    If anyone has an 18T or a 20T sprocket they would like to donate..... :eek: I think the 20T would be about perfect, the 19T was too loose, the 21T was too tight.

    What about gearing, no one has answered that question?

    I have 26" wheels, 1.35 tyres, and the front chain wheel is a 48T, for bombing around town I think the 17T should be about good, maybe a bit of slow grinding on the hills of Tokyo :rolleyes: but with just the bike, no fenders, derailers, rack, etc, it should be nice and light and fun to bomb around on...?

    Cheers!

    PS I've not spent a thin dime on this, everything is from the recycle bin :angel:
     
  20. Phil

    Phil Maximum Pace

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    I don't think there was any doubt that when this Stu first asked this question he would, egged on by kiwisimon and others, end up fashioning something in his workshop to solve the problem... :D

    Nice job, Stu. Always enjoy these threads.
     

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