Originally Posted by
duanedr
My first thought was that the straight gauge tubing forces more of the stress to the end at the lug - as mentioned in the first response. Double butting helps alleviate this by allowing more flex in the middle away from the HAZ/stress risers and thereby lowering the stresses there. More simply, it spreads the flex across the whole tube.
At least that's my understanding of butted tubing vs straight gauge.
there is one builder that is pushing this theory hard, but the reason for butting is very simple, because the haz is weaker. So it needs to be thicker than the center of the tube. That was always the stated reason for it. I don't think that straight gauge pushes that much deflection to the end. I hate speculative engineering, particularly in cases that are not self evident and likely to submit to a good thought experiment. If someone can show me a good fea model of a frame that demonstrates this, then i would be happy. As it is, it's just speculation. And no, a diving board is not a good example.