Shortened Rear End?- Mtbr.com
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  1. #1
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    Shortened Rear End?

    Knowing only that the complete frame is aluminum, and not terribly expensive, what is the consensus on shortening the chainstays?

    Wall thickness is unknown.
    Heat treatment is unknown.
    Exact material is unknown.
    Tubes are not round.


    Does anyone pick A, B, or something else?

    I kinda like A for the increased fudge factor, but B looks stronger.

    Thanks,
    -F

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    It's never easier - you just go faster.

  2. #2
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    C: If you don't know what the material is, you don't know what heat treatment to do after welding it back together. That should be a non-starter. So just don't do it.

    However, if you're capable of executing either A or B safely and making the frame reasonably straight, you're capable of building a complete frame. Not sure what "not terribly expensive" means to you, but a complete tubeset from Nova (steel or Al) can be had for around $150 or less.

    While the first point may have come across as discouraging, I really intend the latter point to be encouraging to build something.

  3. #3
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    Don't do it.......OK?

    Disaster awaits.

    You are looking at this as a project to try some skills on, go ahead.

    Technically, by asking, you need to study this sort of stuff and you will learn that you don't do this sort of thing.

    Eric
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  4. #4
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    Just why, that's what I want to know? How hideously long are the stays to make you even consider doing this to a cheap frame you seem to know nothing about? The whole short stay fad can keep moving on, but at 6'2", I've found that with a Reach in the 470-485mm area, I don't want my stays any shorter than 440mm, all my current bikes are actually at 450mm right now, '13 PP Prime, '08 Monkey, '18 Unit.
    One day your life will flash before your eyes, will it be worth watching??

  5. #5
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    OK OK, I won't do it. Sheesh.

    The stays are 460mm on a fatbike. Based on tire clearance (26x4.8), they could be ~1/2" shorter. If that rode OK, that would be reason to seek that out on the next bike.

    I figured everyone would be asking about welding thin, butted tubes right on the thinnest area or something.
    And I haven't read my heat treating book in a long time, but I thought most of the heat treatments for aluminum (where bicycle frames are concerned) were pretty similar.

    Oh well - my question is answered. Thank you.

    -F

    PS - none of this is in my skill set to begin with - I'd be better off bolting it all together.
    It's never easier - you just go faster.

  6. #6
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    Quote Originally Posted by Fleas View Post
    ...I figured everyone would be asking about welding thin, butted tubes right on the thinnest area or something. ...
    Interestingly, most tapered stays are made in such a way as to make this a non-issue. Generally they're either straight gauge or they're single butted. I'm sure processes vary, but think most tubes are made butted with a constant diameter, and then swaged down on one end to form the taper. As the thinner-walled end of the tube becomes the smaller diameter end of the tube, the wall thickness increases. So even with butted stays, they're often no bad place to weld them because, in the end, there's no thin spots.

    ...Usually.

    Quote Originally Posted by Fleas View Post
    ...And I haven't read my heat treating book in a long time, but I thought most of the heat treatments for aluminum (where bicycle frames are concerned) were pretty similar.
    While most bike frames are made out of 6000-series aluminum, 7000 used to be pretty popular as well. 7000 series tends to be more expensive and I'd guess models that used to be high end aluminum have mostly morphed into carbon. That said, 6000 and 7000 have _very_ different heat treating processes. 6000 is solution quenched whereas 7000 can just be annealed (cooled slowly).

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