Originally Posted by
Scooper
A significant difference between 1030 carbon steel, 4130 chromium-molybdenum (like Reynolds 501 and 525), and Reynolds 531 manganese-molybdenum is the strength - both the ultimate tensile strength and the yield strength.
AISI 1030 - UTS=525 MPa, YS=440 MPa
AISI 4130 - UTS=700 MPa, YS=600 MPa
Reynolds 531 - UTS=803 MPa, YS=695 MPa
Reynolds 953 ultra high strength stainless steel has a UTS of 1,750 MPa and a YS of 1,450 MPa
The stronger the alloy, the thinner (and lighter) the tubes can be drawn. The downside of thin walled tubes, though, is that since the modulus of elasticity of all steel alloys is virtually the same (~200 GPa), the thinner walled tubes will be flexier. In order to make thin-walled tubing stiffer, oversized (OS) tubing with slightly larger outside diameters was developed in the late 1980s. To get really stiff lightweight frames, "double OS" tubing with even larger diameters came to market.
EDIT - There is absolutely nothing "wrong" with Peugeot Carbolite 103 frames. They're typically a little heavier than frames made with stronger alloys, but that's not necessarily a bad thing.
It's a personal thing but I prefer the style of the older bikes from the 80's era, the narrow tubes and the steelwork, it's as if some of the character of their builders has been transposed onto the bike itself adorning it with its own personality (sentimentality overdrive I know). Today's bikes have none of that charm, it's very much like comparing a steam locomotive with a modern electric, there is a reason why my son loves the old engines, it's personality, they have it in abundance.