Scratchbuilding a frame.

Discussion in 'General Questions' started by HackJob, Sep 20, 2007.

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  1. HackJob

    HackJob Guest

    Hi guys,

    Im about to embark on my first frame build.

    so far ive collected old bikes for parts and brackets and so forth.

    I plan to bend up a frame and weld it up.

    ive got a a traditional style 8 speed rear caseete on teh rear wheel but want to ditch it in favour of a single hub that runs gears thru a shifter.

    (sorry i dont know how to describe it.. like an old style 3 speed shoifter etc).

    are these hubs narrower than casette hubs? I want to start setting up my frame but need to know if i can set up using my existing wheels first.

    any help appreciated



  2. Dockspa1

    Dockspa1 Guest

    From the other threads of help in here, I have learned that the internal 3 speed hub, cannot handle the torques produced from the motors. I guess if you are building a wheel burner/ rack mount, then it wouldn't matter as much.
    Just my thoughts
  3. Dan Hunter

    Dan Hunter Guest

  4. HackJob

    HackJob Guest

    thanks Dock,
    good info to pass on before i motor down the wrong road.

    thanks Dan will take alook at the links.

    so does this mean all these planetary type hubs are no good for a frame mount motor?

    what are most of you guys running? just a motor with std type caseetes or..?


  5. DougC

    DougC Guest

    First off, concerning rear hub widths--yes, they are different, for the general different types. A 3-speed Nexus needs about 4.75 inches between the dropouts, a 8- or 9-speed external gear hub needs about 5.25 inches. This particular dimension is called the "outer locknut distance", or O.L.D. for short:
    (follow the link to the "spacing chart", and it tells you which external-gear hubs are how wide)

    The terminology is helpful here--the hubs with 8 different cogs on the back are called "external gear hubs". The multi-speed hubs with just one cog are called "internal gear hubs". Here's a page of Shimano internal-gear hubs, but there's other companies too.

    Lastly--you can't easily build a frame to take both a 8-speed external and an internal-gear hub; the frame's going to be real loose on one and real tight on the other. A a 7-, 8- or 9-speed external-gear will be around 135mm wide. A Shimano Nexus 3-speed hub's specs can be found on the Shimano cycling website, which gives either ~120mm or 127mm, depending on which brake the hub has (coaster or roller).

    As for how you're giong to connect the engine, it's easier to talk about "drive sides"--how the engine is connected to the rear wheel.
    On a normal bike, the chain that runs around the pedals and the rear wheel is on the right side, and engines don't normally use that. Most chain-drive engine setups use a separate sprocket that runs on the left side of the rear wheel, with a separate chain.

    It might help to find a picture of someone else's bike that shows the drive setup you want to do.
    Last edited by a moderator: Sep 20, 2007
  6. Dockspa1

    Dockspa1 Guest

    You can run as many cassett gears as you want under the human power but most use a single speed for dependability. The hub, with or without a cassette is a free wheeler and with or with out the internal brake does not matter.
    I'm pretty sure thats how it goes!
    I have a 7 speed cassette on one of my MB's and just a single speed on the other.
    By the way, I had to find a single speed rim to fit the 1-3/8 tires.
  7. HackJob

    HackJob Guest

    very helpful info guys, I am doing alot of searching and browsing to find the correct terminology.

    thanks for taking the time to explain it to me as well

    ok so I reckon ideally now my motorised bike shoud run a single speed freewheeling hub.

    and I should probably get the correct hub/wheel before getting too excited with the welder.. lol


  8. Alaskavan

    Alaskavan Guest

    On most of these bikes, the pedals are often only used to start off (saves wear on the clutch and stress on the spokes). Hence they only need one gear for the human powered side. My bike has 8 gears on the cassette. I only use 1 of em.
  9. Dockspa1

    Dockspa1 Guest

    I agree again with Van, out of the seven gears, I only use one to start the motor.