Help building a single speed MTB 700c 29er?

Discussion in 'KLUNKERS & MOUNTAIN BIKES' started by yoothgeye, Apr 18, 2011.

  1. yoothgeye

    yoothgeye I build stuff. Moderator

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    A couple years ago after I sold my FS MTB, I was shopping for something else used. I came across a single speed mountain bike and I was really intrigued. It sold before I could get it, but I haven't forgotten it. I went on to get a decent mountain bike, but still think about having a sigle speed for simplicity/fun.

    I'm always picking up free bikes and a few days ago I got a Trek 7100 hybrid/comfort bike. The bike was rough, lots of stuff bent and damage, but the frame is straight, clean, and super beefy.

    Here it is how I found it:
    [​IMG]

    As I was tearing it down yesterday I kept thinking it would be a great single speed, great frame, large diameter tubing, after I removed the suspension seat post, and threw away the street shock, and removed almost everything else, this is what I will be starting with:

    [​IMG]

    I can see my first issue will be the vertical drop outs, but the bike I saw had a rear mounted chain tensioner, it looked like a derailer, but with just 1 cog.

    I have a set of 26" Araya MTB wheels I will be using, and I have a couple new BMX freewheels I can choose from to put on there, so wheels are covered. I have plenty of stems and bars, might have to source a seatpost or cut the suspension one, but that's not a big deal.

    As for a fork, I'd like to go suspension, nothing fancy, but something made for MTB, needs to be a 11/8 threaded based on what else I have to work with, but if I can't find anything cheap to free then I do have an old rigid Tange fork I think I can use.

    The paint is pretty on this bike, but after all the mismatched parts I will be ratting it out a little. so some rattlecan is in order.
     
  2. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    Oh yeah, so if you read all of that, here's the things I need help with.

    -chain tensioner?

    -leads on a fork

    -forgot to mention this, the crankset on the bike won't do. The bottom bracket is great, but I will need new arms and a single gear. Not sure what gear I will go with, maybe around 28-30, not really sure, I think my freewheels are 16 or 17 tooth. So I need advice on the crankset.

    Oh, and I'm SUPER cheap, so keep that in mind.
     
  3. yoothgeye

    yoothgeye I build stuff. Moderator

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  4. cman

    cman Moderator

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    Re: Help building a single speed MTB

    Those singlespeed tensioners will work a little better than DIY.

    Are the MTB wheels you plan on using 26" ? You may run into issues as the brakes won't adjust that much.
     
  5. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    I was wondering about that. The back will be my main issue, if I run that old mountain bike front fork I have (called my friend, he still has it) then I will just use some old center pull canti brakes, I always thought they stopped real good, and I have a few sets.

    I might have to fab u a bracket on the back to lower the mounts, I can think of just the part I have, one of those horseshoe shaped things off a fork.
     
  6. Dr. Tankenstein

    Dr. Tankenstein

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    Re: Help building a single speed MTB

    Clancy,
    Were do you see an issue with modding an old derailluer?
    Chain pitch? You'd have to run a multi-speed chain to move through it smoothly right? Then I guess you'd have to file the teeth on the chainring and/or rear cog a little bit. Would you also have to 'prevent' it from functioning as a derailluer by moving side to side (like while making a gear change)?

    Just asking........you never know.....

    Cheers,
    Dr. T
     
  7. socal_jack

    socal_jack

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    Re: Help building a single speed MTB

    Check out this rant on the Surly page concerning single-speed drivtrains. Done a few conversions and this guy is spot on, also helps explain why the derailleur isn't so good especially if the chainline is off a little bit under load. Although the Surly singulator has many imitators they don't have a push-up mode which is far superior for conversions.

    http://surlybikes.com/blog/spew/spew_single-speed_drivetrains/

    You can eliminate the need for a tensioner sometimes if you can hit the "magic gear" combo, use a calculator like the one below, half-link chains help also. Measure from the centline of the crank spindle to the center of teh rear axle to get the chainstay length.

    http://eehouse.org/fixin/formfmu.php
     
  8. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    OK, I'm thinking mroe about my chainring/crank arms. I have an old Scwhinn mountain bike in the shop with a Shimano Biospace crankset. I was looking at these the other day and thinking of using them, but thinking again, if I do happen to get lucky and get a chain to fit without a tensioner, it won't work on the Biospace will it? (since the biospace gear is oval, not circle)

    But with a tensioner it should work... I guess?
     
  9. socal_jack

    socal_jack

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    Re: Help building a single speed MTB

    A Biopace ring would be alot of tension to pick up on the slack part of the lobe, you'd probably have to compromise on the tension. Ideally, try to use chainrings and cogs without any ramps and pins on them, you can probably get away with using the derailleur if the chain is setup right for street use, wouldn't use it as an mtb like that though if there's any serious hills around.
     
  10. cman

    cman Moderator

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    Re: Help building a single speed MTB

    I was trying to make it look like one of the store bought models with a single wheel. If you just set the limits they would probably work okay.


    Here is what Sheldon says about Biopace and Fix Gears.
    http://sheldonbrown.com/biopace.html
    People are often astonished to learn that I ride Biopace chainrings on fixed-gear bikes. They imagine that there will be tremendous changes in chain tension as the chainring rotates. In practice, this is not the case. A 42 tooth chainring will generally engage 21 teeth against 21 chain rollers, regardless of its shape.
     
  11. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    I need to start scrounging around some more, this Trek and the Schwinn are the only name brand/good component mountain bikes I've gotten my hands on and the Schwinn is Biospace and the Trek cranks won't allow me to run just 1 sprocket.
     
  12. socal_jack

    socal_jack

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    Re: Help building a single speed MTB

    Next paragraph

    "There is a slight variation in tension resulting from the varying angle between the two straight runs of chain as the axis of the chainring rotates, but this has not generally been of a sufficient magnitude to cause any problem in practice for me."

    For a fixie which of course uses no tensioner it probably does feel "slight", still there but not so noticeable to the bike/gear. There is however a force multiplication on the longer lobe sides which line up pretty closely with the crank arms. Tensioners and derailleurs get some very high forces on them, I have mangled my share of cheaper Shimano crap RDs and bent RD hangers going up really steep stuff. From what I remember of my one bike that came with Biopace(Nishiki Ariel IIRC) it did anything but smooth out power delivery especially in the small front ring and was quickly replaced. I'm constantly amazed at how much better chainline alignment, cog chain-wrap etc has to be on my SS conversions than a geared mtb due to torque issues.
     
  13. deorman

    deorman

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    Re: Help building a single speed MTB

    Seems to me it would be simpler and more effective to just add 20 gears. :idea: :mrgreen:
     
  14. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    I've already got a bunch of multi speed bikes. :lol:
     
  15. socal_jack

    socal_jack

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    Re: Help building a single speed MTB

    yoothgeye, I found my old SS conversion tensioner, spacers, and 18t cog, if you want them PM me I'll just mail `em to ya, not doing any good sitting in my toolbox. It's the same cheapo unit you see everywhere under different brands but I did upgrade the jockey wheel. My only advice would be if using a 1/8" chain maybe ditch the guard around the wheel seemed to catch now and then and get the chain as short as you can.

    [​IMG]
     
  16. jan

    jan

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    Re: Help building a single speed MTB

    looking forward to see the finished bike, thinking about making one myself.
     
  17. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    Thanks, I'll keep an update. Got my SS kit yesterday, hopefully my friend will visit and bring my fork soon, I think before that though I need to get him to measure it to make sure it'll fit the steertube. I can leangthen 1" forks pretty easily, but haven't tried with a 1 1/8".
     
  18. Walker

    Walker

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    Re: Help building a single speed MTB

    Same process for lentghening a 1" or 1-1/8", I'd strongly recommend making an iternal sleeve though.
     
  19. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    Yeah, that's how I've lengthened 1", with an internal sleeve, there is a size of gas pipe that slides in very snug and welds clean.
     
  20. yoothgeye

    yoothgeye I build stuff. Moderator

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    Re: Help building a single speed MTB

    Bringing this thread back to life (I hope) all other builds have been trumping this one, but as more parts come in and I've been trail riding more, I still want the single speed.

    Here's where I'm at. I did a trail ride last night and I settled into a gear and stuck with it, climbs, flat, downhill, even the street on the way home. 34/18, man, I'm loving that ratio.

    So, when we got back from the ride (about 2:30am, haha) I looked and I have an 18t freewheel. Now, here's where help is needed now. Still trying to do this on the cheap, I only have 1 crankset where the chainrings are removable, it's on an old Schwinn MTB. They are Sakae FX crank arms running Biospace rings. The middle Biospace is a 38 tooth and I can't do that. Will the Sakae crank accept regular round chainrings? If so, what am I shopping for?

    I think the egg shaped Biospace rings causing an optical illusion making the bolt pattern on the crank arm look egg shaped, but when I measure center of allen bolt to center of allen bolt they are approximately 2.5" apart, no noticable variation between any of them. If all I have to do is buy a cheap chainring then I'm set. Help!!!

    $10 for this 34 tooth ring, will it work?: http://www.amazon.com/Shimano-Ultegra-F ... 822&sr=1-1
     

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