Bicycle Mechanics - Straight Gauge vs. Butted Tubes
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10-06-09, 05:31 AM
It makes sense that butted tubes would be lighter (as they consist of less metal): http://www.desperadocycles.com/The_Lowdown_On_Tubing/About_Steel_Tubing_page3.htm
But are they stronger than straight gauge?
Granted, a tube with a consistent inner and outer diameter is heavier, but is it less able to resist tensile strain than its butted counterparts? Or is it all just a matter of weight?
10-06-09, 07:53 AM
It's not any stronger if the straight tube is at least the same thickness as the thickest butted end. As you can read in the quoted article, butting basically puts material where it is needed and eliminates it where it is not.
To get stronger, you'd need to use splined tubes like the late 80's and early 90's Miyata's. See this (http://2.bp.blogspot.com/_whtVpXkKwlQ/R2CefjQprjI/AAAAAAAAAl8/U2hJCUT0O3E/s1600-h/img257.jpg) page from their 1991 catalog for an explanation.
10-06-09, 08:05 AM
Obviously staight guage tubing is stronger than butted but as the previous poster notes it's strength is not needed in certain palces. Hence, straight guage tubing IS stronger than butted tubing, but a FRAME properly made of butted tubing should be just as STRONG as a frame made of straight gage tubing.
The frame made of straight guage tubing would however be stiffer.
10-06-09, 08:40 AM
A straight gauge frame will be stiffer, heavier, and better able to withstand denting in the middle of the tube compared to a butted frame. Butted frames will be just as strong in terms of resisting fatigue failure at the joints, lighter, and will ride more smoothly since the tubes will flex more.
10-06-09, 09:45 AM
Thanks for your answers =)
10-06-09, 09:55 AM
Absolute strength isn't an issue with bike frames. They don't fail by pulling apart at the middle of the tube.
Butted tubes can have the same or better tensil strength as straight gauge tubes since they are usually made from a stronger alloy steel.
Are butted tubes stronger?, short answer -- depends.
Strength comparisons between butted and plain gauge tubes is a tricky issue. Butted tubing wasn't originally used to save weight per se, but to compensate for strength lost at the heat affected area, (brazed or welded). The thinner section allowed more flex away from the ends and resulted in fewer joint failures. This is analogous to how using butted spokes makes wheels last longer.
So while the removal of metal makes a frame less rigid, the added resiliency makes it more durable. Whether it's stronger is a matter of defining strength, as either rigidity, maximum load capability, or durability in real world use.
It's like comparing the strength of oak trees and willows. Oaks are obviously stronger, but willows do much better in hurricanes.
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