Another point that I mentioned before, there was always an urban bicycle myth that Reynolds 531 tubing was lighter than Columbus (SP) tubing.
Many production bikes built from the early 70s through the early 80s used Reynolds 531 7/10 wall thickness tubing.
That's the same 7/10 wall thickness as Columbus SP tubing!
The links below show some pages from the 1980 Gitane catalog for their top of the line Olympic model. The spec sheet is in French but you can see the 7/10 reference:
http://tinyurl.com/
What I've heard over the years was that back in the day a pro racer only had 1 or 2 bikes for the whole season; they were usually made out of heavier gage tubing to survive crashes and handling abuse between stages.
Another factor, an economic one, I suspect that many bike manufactures used heavier gage tubing in their production bikes because they could employ less skilled workers to braze up the frames thus work faster. Also these frames were less likely to get dented during the manufacturing process.
Chas. Colerich Oakland, CA USA
Bill Roberts wrote:
> Interesting post Chas, thanks.
>
> Regarding it being a somewhat common build trick to use the thicker wall
> Reynolds 531 seat tubes in 70's English bikes. Many 70's Ron Coopers indeed
> seem to be this way (27.0 post), in sizes 58c and larger. Versus a 27.2 in
> 57c and below. Sheldon Brown agreed this was intentional (tubing
> selection). I've noticed this on several of Ron's frames. With Ron being
> very meticulous in both design and execution, I expect it is intentional,
> and the thicker tube was used.
>
>
> Bill Roberts
> Jacksonville, Oregon USA