I was a framebuilder for over 20 years; working with your hands all day every day keeps 'em pretty strong, but I was never able to permanently dent the thinnest 753 by hand. Even the thinnest Tange Prestige, at 0.3mm (0.012") only 3/4 as thick as the thinnest 753, would flex noticeably but not permanently dent, hard as I tried. I have to say I think it's a myth that anyone ever dented a bike tube with their hands - unless it was turned to lace by rust!
Greg Parker wrote:
> I've also heard a story of a brazed-on shifter and its boss being
> pulled off of a 753 DT on a Cuevas, leaving a fatigue-type hole!
> (Too much heat perhaps?)
Cuevas was vocal about his belief that brass brazing was proper for 753. He must have sent Reynolds a silver-brazed sample to get certified, but then he made all his frames (as far as I know) with brass. I have done instrumented crush testing of frames, and I can tell you for sure that quenched-and-tempered low-alloy steels like Prestige and 753 can be strong enough despite their light weight, if the heat is kept to a minimum. In many cases the thinner heat-treated tube (753) was stronger than the thicker normalized tube (531). But brass brazing on the thin unbutted part, like the Cuevas shifter boss, is asking for trouble. The initial crack may well have even started during brazing.
Since the middle of the tube where you're sitting usually hasn't been heated much, at most only a tiny cable housing guide that's almost certainly silvered on, it's safe to say: Garth, go ahead and sit on your top tube. Just don't quote me out of context... ;^)
Mark Bulgier
Seattle, Wa
USA