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  1. #1
    Newbie
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    Dec 2011
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    Bottom Tube Sizing?

    Years ago, I built bikes with old parts. It was huge fun, but then life got in the way (school, job, etc.) 30 years later, I am starting to build frames/bikes again. Now though, my goal is to build side by side tandems and velomobiles that my wife and kids will actually ride in with me. So here is my first newbie/old man (the times have changed) question:

    - I can do the math and calculate bottom tube sizes, but does anyone have any "real world" experience or rules of thumb for sizing 4130 bottom tubes for LWB recumbent bikes?

    Stiffness will obviously not be an issue for a side by side tandem going 5-10 mph around the neighborhood or down a flat bike path; I just don't want to add any more weight than absolutely required, but don't want to have a "bent bent" every time I hit a small bump in the road...

    Thanks in advance for any help/advice,
    Joe P.

  2. #2
    Insane Bicycle Mechanic Jeff Wills's Avatar
    Join Date
    Mar 2008
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    other Vancouver
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    "Stick bike"? Multiple tubes? Space frame?

    IMO, a single tube between 1 1/2" and 2" in diameter will be more than adequate, especially if it's used for low-intensity riding.

    What kind of side-by-side (usually called a "sociable") design are you going to build? 3 wheels? 4?
    Jeff Wills

    All my bikes.

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