Thread: Curved top tube
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Old 04-03-07, 08:16 AM
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Originally Posted by AllenG
What are the ramifications of a curved top tube, like those found on cruisers? Are they significantly weaker than a straight tube? Same questions about curved seat stays.


When Frank Schwinn patented the frame design popularly known as the "cantilever frame" in the late thirties, the claims made in the patent were that the two small diameter curved tubes welded to each side of the down tube, then carried back to the seat tube where they are welded to each side the seat tube near the seat post clamp, and then finally transitioned to become the seat stays, "...resist certain strains, resultant from accidental or other overloads, which frequently destroy other bicycle frames, - i.e. those strains which tend to twist the axis of the steering head (now called the head tube - Stan) out of the plane which includes the axis of the saddle post mast (now called the seat tube - Stan), and those strains which tend to disrupt the union between the steering head and the reach tube (now called the down tube - Stan) which, in the normal use of the bicycle, constitutes a tension member acting between the steering head and the crank hanger."

It is no accident that the first home made "mountain bikes" were built using these extremely rugged frames.

- Stan

my bikes

Science doesn't care what you believe.

Last edited by Scooper; 04-03-07 at 12:34 PM.
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