Gears???

Discussion in 'HOW TO' started by BikeBuilders, Jan 10, 2012.

  1. BikeBuilders

    BikeBuilders

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    Just a little curious about something here.... I have done a lot of reading, and a lot of lurking here.... You guys do some amazing stuff. And I love the fact that building bicycles is a WHOLE LOT cheaper than building motorcycles. Perfect hobby for me.....

    What I have seen is that some of these custom built bikes can end up being pretty darn heavy. Not so much the bikes here that I have seen, but on another site. Chopper bikes with big back tires to be exact. I like that style.

    So, onto my question.... With all of the amazing things I have seen you guys do, why is it that all of the bikes I have seen remain single speed? Seems like it would be easy enough to at least add a rear derailer. This would give you at least a few gears. Even if you left the front a single sprocket only. I am sure there is a logical reason, just wondering what it is before I head down a road doomed for failure.

    So what's the reason? Mechanically unadvisable, personal preference, oversight on my part????

    Thanks
    Rob
     
  2. cman

    cman Moderator

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    Most like the simple style of a single speed coaster brake. No cables for brakes or gears.

    3 speed internal geared hubs are popular or 2 speed kickback hubs.
     
  3. BikeBuilders

    BikeBuilders

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    That makes sense.... A cleaner look. But in the event I wanted to use a rear hub from say a 21 speed mountain bike, and the rear derailer (and possibly even front), there is no mechanical or other unforeseen reason it wouldn't work???? Or any experienced builder warnings, tips or tricks I should know about?
     
  4. jalopyjimmy13

    jalopyjimmy13

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    cable length :idea:
     
  5. BikeBuilders

    BikeBuilders

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    Understood.... Any other words of wisdom, warnings or tips???
     
  6. udallcustombikes

    udallcustombikes Moderator

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    I built my Monster Trike using an 18 speed gearing to spin the 31" Coopers.
    [​IMG]

    One problem you may encounter with a wider rear tire is your chain line. If it is an issue you can employ a jackshaft compensate.
     
  7. Dr. Tankenstein

    Dr. Tankenstein

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    Another thing to consider is the chain pitch. You have to switch your front sprocket from 1/2 x 1/8" pitch to 1/2 x 3/32" in order for smooth/proper operation.

    Good luck!

    Cheers,
    Dr. T
     
  8. BikeBuilders

    BikeBuilders

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    Forgive the newbie question, but what is "chain pitch"??? Please explain....
     
  9. kingfish254

    kingfish254 Check out the 30+ Items in my FOR SALE thread! Pro Member

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    Chain pitch is the distance between chain rivets. Almost all modern chains are 1/2 pitch.

    The 1/8 and 3/32 that Tank refers to is the Chain Width (between two inner plates). Single speed and three speed chains are typically 1/8. Deraileur bikes are typically 3/32.
     
  10. wheelymarko

    wheelymarko

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    I like simplicity! Mine is a coaster brake triplespeed. :roll:
     
  11. wimpy

    wimpy

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    Mine too. And I used an 80 mm backrim (not wider),so I didn't have to alter the standard sprockets into off-set sprockets,because of the chain clearance. Any other wide(r) rim brings along the problem of how get the chain from front to back,in a straight line. So I chose the easy way.
     
  12. DGuff

    DGuff

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    Another thing to look at is the spacing of the hub itself. Most coatser hubs have a 118mm to 120mm spacing so the frame is built to match. A 6 spd or greater hubs spacing starts at around 125mm and go up to 135mm so you would have to spread the rear chainstays to make it work. Not a real big deal until but something to look at.
     
  13. BikeBuilders

    BikeBuilders

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    Gotcha.... But if I use all the components (rear hub and sprocket, front spocket and chain) from the same donor bike, I won"t have to worry about changing anything, right??
     
  14. Dr. Tankenstein

    Dr. Tankenstein

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    Yep, that'll work. Just be aware, most older and newer, single speed bikes use a one piece crankset, like this;
    [​IMG]

    Now, if you can find a donor with a multi-speed rear, one piece crankset front, you're good to go.

    However, if the donor has a three piece crankset (which most modern mountain bikes, BMX bikes, etc...use), like this:
    [​IMG]

    You'll need to get a US-euro conversion kit, like this:
    [​IMG]
    http://www.amazon.com/BB-Conversion-Bp-American-To-Euro/dp/B001G8TSPS

    Good luck, keep asking questions, there's a LOT of knowledgeable people on here! :wink:

    Cheers,
    Dr. T
     
  15. BikeBuilders

    BikeBuilders

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    Thanks, but now I am confused.... If all parts come from the same donor bike, why would I need a us/euro conversion? Seems like all I would need to do would be lengthen the chain if necessary.
     
  16. wheelymarko

    wheelymarko

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    The conversion is just another way of doing it :)
     
  17. Dr. Tankenstein

    Dr. Tankenstein

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    Sorry, I just re-read that, it was a little confusing, even to me.. :roll:
    Basically, it all depends on the frame you using for your bike (not the donor).

    Typically, newer frames that utilize a 3-piece crank with multi-speed rear hubs have a smaller bottom bracket tube compared to the 'classic' single speed frames.

    Now, if you can find a vintage '5 speed' donor bike with a single front sprocket, a 1-piece crank and a multi-speed rear, then everything should move over to the 'final' frame with no problem.

    If you find a 'modern' donor, like a mountain bike, with a 3-piece crank (the number of sprockets is irrelevant) and a multi-speed rear, chances are you'll need the bottom bracket adapter. The adapter reduces the internal size of the bottom bracket tube down from a 1-piece size to the modern (or euro) 3-piece size.

    Hope that makes more sense.. :D

    Cheers,
    Dr. T
     
  18. meatwad1

    meatwad1

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    Hmmm... How do I explain this where someone who has done such a thing will not try to argue with me on their reason for doing so? This will be a challenge.

    If a bicycle is so unergomatic , so heavy and so inefficent that its top speed is only slightly more than a crawl then having multiple gears on it is redundant. Finding a comfortable gear ratio for such a bike I imagine is a very specific task. Having multiple gears on one is pointless.
     
  19. gcrank1

    gcrank1

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    It is the nature of man to find a complicated solution to a simple (or, as some would argue, a non-existent) problem......... :wink:
     
  20. meatwad1

    meatwad1

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    Sure is. Thankfully when I have done so I can pass it off as artistic license. Thank God for Rat rod bikes :)
     

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