Andrew Gillis wrote:
[snipped]
> Since most seat tube thicknesses were relatively constant
> (around 0.9 mm for Columbus SL.) the seat tube's outer diameter
> would then vary proportionally to the seat post size.
Other than a few rare oddballs, there were only 3 seat tube diameters in the classic era: 1" (American heavyweights), 28mm (French), and 1-1/8" (28.6mm - everyone else).
Wall thickness really does vary a lot, but is seldom 0.9mm where the post goes in, on the lightweight frames we CRs like. Col SL for instance is 0.6 at the top.
Lugless frames often have a DB seat tube (and thus smaller post), but lugged frames almost always have SB. Manufacturers almost always shorten the tube to size from the top only, but there still isn't always enough butt at the bottom to reach up to the derailleur clamp, so denting may indicate clamping on the unbutt. Either that or a ham-fisted mechanic. (Ok I've dented a couple - musta been defective frames)
Mark Bulgier
Seattle, Wa USA