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Old 11-14-2013, 03:33 PM   #1
mymonkeyhasboobs OP
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Rectangular tube orientation

I've read about torsional forces in sidecars but am unclear how it relates to frame design. I know round tubing is best, but I have rectangular, and to be honest I find it much easier to work with given my skills and tools. I have some 2 1/2 x 1 1/2" aprox. .09 I will be using. When people talk about torsional stresses are you referring to the force of the sidecar trying to hold the bike upright or the load that happens when your sidecar wheel drops in a pothole and tries to tear the hack off the bike towards the rear? Or both? When using rectangular tube for a frame, would it be better to use it with the wider side laterally (taller) or horizontally (wider)?
I plan to run a sway bar if that matters at all.
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Old 11-14-2013, 04:16 PM   #2
Warin
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I'd use it "taller (vertically)" ... as you can add more strength horizontally by cross bracing than you can add strength vertically (given the usual dimensions of a chair). Also makes mounting suspension and swing arm easier.
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Old 11-14-2013, 05:00 PM   #3
claude
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I think with the material you plan to use you could stand it up or lay it down. I would probably stand it up as it would make adding mounts easier especially the lower ones if you are using a tube inside a tube type arrangement. You could also run the swaybar through the rectangular tubing if done right. Note that Motorvation and Texas sidecar have used rectangular tubing for years with good results.
Gusset the connections and don't be shy on adding bracing here and there.
Yes, round is better on all planes but that doesn't mean it is the only way to go.
We use 1 1/2 x .120 wall round D.O.M. on most of our chassis designs. Most welding is via T.I.G. today.
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Old 11-14-2013, 09:19 PM   #4
davebig
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Quote:
Originally Posted by mymonkeyhasboobs View Post
I've read about torsional forces in sidecars but am unclear how it relates to frame design. I know round tubing is best, but I have rectangular, and to be honest I find it much easier to work with given my skills and tools. I have some 2 1/2 x 1 1/2" aprox. .09 I will be using. When people talk about torsional stresses are you referring to the force of the sidecar trying to hold the bike upright or the load that happens when your sidecar wheel drops in a pothole and tries to tear the hack off the bike towards the rear? Or both? When using rectangular tube for a frame, would it be better to use it with the wider side laterally (taller) or horizontally (wider)?
I plan to run a sway bar if that matters at all.
The reason they use allot of retangular or square is it's easier to get a miter on the corners, cold saws do nice 45 degree cuts and theres not all the notching, grinding easier. They can also have their storage racks full ot precut stuff to assemble as needed.DB
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Old 11-15-2013, 07:24 AM   #5
claude
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Quote:
Originally Posted by davebig View Post
The reason they use allot of retangular or square is it's easier to get a miter on the corners, cold saws do nice 45 degree cuts and theres not all the notching, grinding easier. They can also have their storage racks full ot precut stuff to assemble as needed.DB
No doubt that mitered corners whether round or square tubing are better from a production standpoint. Yep that is why it is done.
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Founder: Internet Sidecar Owners Klub at SCT
http://autos.groups.yahoo.com/group/SCT/

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http://autos.groups.yahoo.com/group/...rsandTrailers/

http://freedomsidecars.com/
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Old 11-16-2013, 08:33 AM   #6
mymonkeyhasboobs OP
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Thanks all, very helpful.
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