Originally Posted by
Road Fan
The engineering properties of the two steels (531 and early Columbus CrMO) are very similar in terms of elasticity, which is essentially inherent material flexibility. Tube sets of the same material should test pretty much the same in terms of flex if the diameters and wall thicknesses are the same. Modern steels are stronger but not stiffer. They allow making a thinner-walled tube, which in the classic diameters will make a lighter and more flexible frame. If the diameter is increased it will make a lighter frame that could even be stiffer than vintage SP.
Stiffness is not really the elasticity of the steel, but the design of the tubes, which is constrained by the strength of the steel.
This assumes all other things, such as joining quality and frame design, are equal.
I can confirm this with my Davidson crit bike--lugged steel (Tange Prestige) with OS downtube, OS top tube, chainstays that are actually fork blades size wise, and a seat tube flared at the bottom. Bare frame is under 4 lbs and the ride is as rock solid as a track bike, in both the good and bad senses (therefore my other bike is a Vitus!).
Steel runs into a wall thickness limit, called by framebuilders 'the beer can ratio' where tube diameter to wall thickness exceeds 50:1, and the tube becomes prone to buckling. My bike's top tube is at 70:1, and has some handling and transport dents. Down tube is at 60:1, no dents yet.