Converting Mtb To Road Bike - What Can Do Wrong?

Discussion in 'Cycling Equipment' started by VladiPHD, Apr 7, 2015.

  1. VladiPHD

    VladiPHD New Member

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    Hi guys, I was wondering if you could give me some help and tips on a project!

    I found an old mountain bike in my parents garage that I want to convert to a single-speed road bike. I would buy one, but I'm 6'5 and frames for me are hard to find, and I also really enjoy doing the work! This frame size is perfect.

    The challenge with this frame is that is it has vertical slots for the hub/wheels which would make it hard to get the chain tension right. I think making it a fixie is not possible because of this, so single-speed it'll have to be. Here's my plan and please feel free to poke holes in it and tell me where I might encounter problems:

    I took everything off the bike besides the brakes. The the rear wheel is a freewheel hub, so I'm planning to get a new wheel that's the same size but has a cassette hub. It's 26 x 1.5 in size.

    So assuming I want to use the same crank and cogs with the pedals, I'm planning to get a small gear for the back and get the chain line straight by stacking some spacers on the hub. Then I'll need a chain tensioner where the derailleur used to be and a 3/32 chain to close it all together.

    So here are my questions:

    Does this sound doable? Is there something I'm blatantly overlooking?

    Are there road tires that will go well with that wheel size or will they all be large mountain-bike size?

    I saw the small rear cogs for the cassette hub and the tensioner at a local bike store, but I don't know the official names to look online. What are those called?

    Thanks for any help and excuse my lack of knowledge or terminology, I did lots of research but I'm sure I sound a bit stupid at some points! I can upload some pics to this post when I get home later.
     
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  2. dabac

    dabac Well-Known Member

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    It's entirely doable, but IMO you're at risk of spending a lot of effort on making the bike LESS useful.
    Maybe more "good looking" to you but less useful.
    More fashion statement than utility item.
    But at least it's not a fixie.

    In terms of everyday use and knee-friendly less isn't more, less is less. There is a reason why gears were invented.

    Me, I'd clean and relube, replace fit and wear items as needed then ride it until something breaks.
    If it's the rear axle, I'd replace with a cassette wheel THEN, scrounge up a matching shifter/cassetter combo and keep riding.

    The driveline on multi-speed bikes are designed to derail.

    Unless you replace the crank - or at least the ring of your choice - you're at risk of the chain coming off frequently. SS rings have higher teeth.
    You may need to buy a chain guide, at which point you might just have left the front derailer in place instead. Same function, no purchase.

    Unless the crank has riveted rings, you can move the big ring to the inside of the carrier for a closer chainline.
    Well, it's doable with riveted rings too, it'll just take more effort.
    And - good frame fit or not - riveted rings, f/w rear, those would be signs of a low-end bike. Make sure it's really worth the TLC that's about to be bestowed upon it.

    If you want an SS, why buy a wheel with a cassette hub?

    Unscrew multi-speed f/w, mount SS/BMX f/w with the desired tooth count. Fiddle around with spacers and washers to recenter the wheel, redish and you're done. The recenter7redish will pretty much "cure" the problem of axles bending/breaking that were the reason for going to cassette hubs anyway.

    And why buy a chain tensioner when you already have a derailer? Apart from the ability to move sideways, maintaining chain tension is what RDs do.

    Either use the limit screws to park the derailer where it needs to be sideways. Or cut a short length of housing, stick it in the derailer's Barrel Adjuster, thread through a piece of shifter cable with the anchor button right up against the housing. Clamp the cable with the derailer where it needs to be, use the BA to fine tune.

    You can get smooth and skinny tires for 26". HUtchinson Top Slick are my favourites, WTB slickasaurus is nice too. Conti Sport Contact a decent option, Geax Street Runner not that fun.
    Check here for how skinny you can go:http://sheldonbrown.com/tire-sizing.html#width

    Going all-out with a drop bar conversion is doable too. But since flat bar bikes often have a proportionally longer top tube, it ca be a bit tricky to get the fit right. And you'd need to pick the right brake levers for whatever brakes you're running.
     
  3. VladiPHD

    VladiPHD New Member

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    Thanks for all that! Huge help!

    Very good point on just switching out the multi-speed cogs for a single speed/BMX cog on the same rear hub. I do have riveted rings on the crank (yes I did buy the bike for cheap years ago). So if that's the case, will I be able to get the chainline straight between the new SS cog and the large cog on the crank? I was under the impression that that's why I needed the cassette-hub wheel because the largest cog on the crank is farther out.

    I know it's a bit hard without seeing the bike!

    And I will definitely try using the derailleur I already have to tension the chain. Thanks again for the help!
     
  4. dabac

    dabac Well-Known Member

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    A multi-speed freewheel wheel and a multi-speed cassette wheel will both have the smallest sprocket at the same distance from the inside face of the locknut. The advantage of the cassette wheel is that it's a stronger design, with the wheel bearing further out.
    But if you can Re-center and redish a freewheel wheel you can reduce the length of exposed axle, and with that, reduce the advantage of the freehub design.
    The common approach for people who want to use the big ring is to move it to the inside of the carrier to improve the chainline. But maybe you'll be happy with the gearing offered by using the middle ring, and the smallest possible SS freewheel?
     
  5. alfeng

    alfeng Well-Known Member

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    With the understanding that MY idea of "an old MTB" would date to the early 90s with a steel frame ...

    What is the material which your bike's frame is made of?

    What is the length of the virtual top tube?

    What is the size of the fork's steerer?

    Were you planning on building it with Drop handlebars?

    Does the frame have an English threaded BB shell?

    Are you open to installing 700c wheels & tires?

    700c wheels/tires can be fit in any MTB frame ...

    Brake reach can generally be accommodated with LONG REACH (49mm-59mm) Road brake calipers.

    FYI. You can use a "half-link" to accommodate chain tension ... you will need an 1/8" chain ... much of what you may want is available from danscomp.com ... so, if you really want to build a Fixie, then you could (I wouldn't, however).

    If you can, then post a picture (or two) of the bike frame and/or crankset/BB ...
     
  6. garage sale GT

    garage sale GT New Member

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    Every so often the local craigslist has an ad for an old 1970s or 1980s road bike with a 25" or larger frame. Keep an eye out. Maybe you'll find something you like.

    The wheels can be plenty strong if you get them tensioned and trued.
     
  7. VladiPHD

    VladiPHD New Member

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    Thanks for all the help guys! I'm gonna try a few of the suggestions over the next few days and document any disasters/successes. I'll upload pics too!
     
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