Framebuilders - Decidng tube strength

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Cadd6
09-28-07, 03:36 PM
I'm planing on building a tadpole trike. I would like to know how to find tube diameter and thickness for frame load of 500 lb. The commercial trikes list a load limit of 275 lbs. At 6' 2" and 340 lbs. plus gear I don't want to find myself bottoming out on the road. Thank you.

NoReg
10-01-07, 11:38 PM
That is a pretty minimal adjustment. If you are worried about stiffness/sag, and figure strength will follow along, then devide the 340 by 275, and take the cube root of the result. That is the percent increase in overall size, with the same proportional wall thickness, you would require, very roughly. Of course that exact tube may not exist so use reasonable judgement. also keep in mind that your weight only affects a relatively short proportion of the beam. Possibly just stiffening up some brackets or seat elements would be enough
Cadd6
10-04-07, 01:08 AM
Thank you, Peterpan1,
I agree that it is a minimal adjustment, but an adjustment from what base. I don't want to give the impression that I know anything about framebuilding. Where would I find basic information?
I have a conceptual gap. On one side I can calculate deflection loads. On the other side I have a table from a steel supplier. I have yet to see how one relates to the other.
I'm looking for something. Maybe a table or chart that says 36" of 1" round 4130 tubing and wall thickness of .049 will support 500lbs without bending.
I'm not reading with a knowledgeable eye. This isn't my usual line of work. :)