Originally Posted by
pwyg
Most Reynolds tube sets came with a 1/2" short piece of 531 for bridges. So short of the manufacturer using another type of steel I most likely is 531
Not sure I agree. Production factories didn't source the tubing in neat sets/kits. Often they had bulk packaging of top tubes than another for the seat tubes and on. Also it's far more cost effective to just chop off a section of bridge tube from a length, over and over, that likely started as a 12" length (the common from the mill length that steel is shipped as). Now as to what this bridge tube steel might be is anyone's guess. I've seen everything from seamed tubing (with barely the seam actually closed up) to what seems to be high strength and thin wall stock.
In bulk a factory can get 1/2" 4130 tubing for a few dollars a foot (and a lot less back in the day). This bulk tube is far easier to handle and store then chasing tiny bits out of hundreds of poorly made cardboard boxes.
To shift to another post- What are the stays made of when only the main frame claims to be 531? Again just about anything. But as stays are tapered these generally would come from a bike tubing processor. (Which BTW is what Reynolds is, they don't actually smelt and alloy the raw rods that 531 is drawn from). Not much cost savings is had with "lower grade" stays given their sourcing. Depending on the bike brand's view using Mangalloy (which is a well made mid grade of steel) or a lower grade like 1020 is a fair choice. Remember that the stiffness of steel alloys is almost exactly the same given the same wall and tube diameter. Since stays don't see much bending a lower strength is a fair choice too. The weight difference of a lower grade stay with a slightly thicker wall and a high grade stay with a thinner wall isn't very much.
Back in the day I remember weighing a Raleigh Super Course frame and an International frame. The SC had 531 straight gage main tubes with unknown stays, the International had a full butted 531 set. The weight difference was only around a half pound or less. (a tad less then 10% IIRC). The weight differences with the components kits was far greater an amount, far greater.
A last tangent- Butted tubing is more flexible then straight gage, for the same weight. We used the term "resiliency" to describe the ability to be strong enough to stand up to the forces and yet be able to flex for a comfortable ride. We felt that a frame needed to be flexible or it would be considered "dead". Which is what I feel many modern bikes are. Andy.