[python] Re: New Jetrike Rev B Plans

  • From: "25hz" <25hz@xxxxxxxxxx>
  • To: <python@xxxxxxxxxxxxx>
  • Date: Sun, 14 Jan 2007 21:28:46 -0500

Actually, I wouldn't say that.  For most of the loading that goes on with a
bent, it's bending stress that is the primary loading type, not torsion, so
square has a 40% strength advantage while only a 20% weight advantage.  You
can't artificially add 40% strength to a 10 lb frame, but you can lose 2lbs
by simply trimming down the rider, or the 2lb weight penalty can be negated
by the rider getting stronger.

The availability of round tubing for bike frames and the fact that bikes
used to be made predominantly of round tube for more historical, commercial
and political reasons than anything to do with strength compared to square
tube.  There is also the aesthetic factor to consider of round over square.
Personally, aside from the ease of fabrication you mention for square
tubing, I enjoy the comments of people who say my bents look "boxy" or
"industrial" or more derogatory terms when they first see them.  After the
rides and races though, they usually don't have so much to say about the
shape of the tubing . . . mind you that's AFTER they catch up to me, so
maybe they don't have enough breath for stupid comments about meaningless
details?  :)

Round tubes, especially in pedal powered vehicles, are slowly being
supplanted by shapes that are better engineered to maximize strength in the
areas and dimensions they are needed and minimized in the areas they do not.
Something else to remember is that most of the bicycle tubing is proprietary
and non-standard sizes and has inflated prices for nominal sizes that are
similar in size and strength.  This is not about volume either, this is
about inflated prices in a quasi-specialized market.  I'll stick to square

----- Original Message ----- 
From: "Carl Punton" <carlpunton@xxxxxxxxx>
To: <python@xxxxxxxxxxxxx>
Sent: Sunday, January 14, 2007 2:01 PM
Subject: [python] Re: New Jetrike Rev B Plans

I think its probably safe to say that round section is the best compromise
of wight versus  strength ,  its pretty much standard for bicycle frames &
various other vehicles that I'm not allowed to mention !  There is a reason
for this , its not just coincidence.
The fact is , our homebuilts are easier to build with square ,  yes , round
would be lighter for equal strength ,  but much harder to align & join ,
hence the slight weight gain is usually accepted.


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