Classic & Vintage - Cheap steel tubing...

If you search you'll find there are enough threads on high-end steel tubing to weave your own tapestry but nobody talks about the cheap stuff despite the fact that it's on 90% of the bikes out there. Everybody lumps it all together as "gas pipe" but there must be some differences to explain why some gas pipe bikes weight 45-lbs while others weigh 27-lbs and it can't all be components. So what's the difference between low-carbon and hi-carbon steel? 1010 vs. 1020 steel. Mangaloy? House brands like "Tube Special Allege Peugeot" or Carbolite or HLE? What's special about that tubing that they felt the need to put decal on the frame? What about the welded frames on old Murrays and Huffys vs. lugged, brazed construction on entry level European bikes?

I like to think of the 531 and Columbus frames of the day as being equivalent to those on $7000+ bikes today, the top of the line. Surely everything else wasn't gas pipe with nothing in between.

none of it was gas pipe. That stuff wouldn't work very well, and a frame would be measured in 10's of pounds. that said, the non-butted standard tubesets for low end bikes was nothing that you'd want to brag about. Low carbon steel is not very stiff, and requires more material to be suitable for a bike frame. That would be roughly why all of the cheaper stuff is relatively heavy (and not so flexible). The cheaper tubes were rolled from sheet stock instead of drawn from solid material, so they also have a seam. That seam is weaker than one-piece steel, and subsequently requires more material to get a safety margin for this application. like before, more material => heavier bike.

People like stickers with cool names like Carbolite, though. Girls want to check out a guy with cool stickers, huh?

none of it was gas pipe. That stuff wouldn't work very well, and a frame would be measured in 10's of pounds. that said, the non-butted standard tubesets for low end bikes was nothing that you'd want to brag about. Low carbon steel is not very stiff, and requires more material to be suitable for a bike frame. That would be roughly why all of the cheaper stuff is relatively heavy (and not so flexible). The cheaper tubes were rolled from sheet stock instead of drawn from solid material, so they also have a seam. That seam is weaker than one-piece steel, and subsequently requires more material to get a safety margin for this application. like before, more material => heavier bike.

People like stickers with cool names like Carbolite, though. Girls want to check out a guy with cool stickers, huh?

All true. I spent a few summers and Christmas vacations working with my uncle who was a plumber so I've worked with actual gas pipe. That said, the welded frame on an old Murray or the electro-forged frame on a Schwinn is significantly heavier than the lugged frame on a low end Peugeot or similar bike from the seventies and the 80's bikes were even lighter. My '85 Peugeot with HLE tubing weighed 24-lbs - not much more than a high-end bike with the good stuff.

What I suspect is that it's not so much about the strength of the raw tubing but rather the ability of the tubing to withstand the joining method. The actual steel used might have been the same (something I'm hoping someone might answer here) but the heat of welding or electro-forging probably weakened it so much that very thick tubes had to be used to make up for that. I measured the seat tube on my UO-8: it's 28.0mm outside diameter (French) and 26.0mm inside diameter or 1.0mm thick walls. That might not be as good as 531 Professional but it's not horrible. I wonder how thick the tubing is on a Murray or a Schwinn or similar bike?

The 70s Raleigh Grand Prix with 1020 tubing had "normal" 1-1/8" outside diameter seat tube, and takes a 25.4 mm (1") dia. seat post. So the wall thickness is: 1/16", minus a tenth of a mm for clearance = 1.5 mm.

The 70s Raleigh Grand Prix with 1020 tubing had "normal" 1-1/8" outside diameter seat tube, and takes a 25.4 mm (1") dia. seat post. So the wall thickness is: 1/16", minus a tenth of a mm for clearance = 1.5 mm.

Interesting. So maybe "Tube Special Allege Peugeot" is special.

Quality mild steel tubing(1020 or 1060)is fairly thin gauge, and usually has a very light seam. Cheap, really cheap tubing like that used on very cheap department store brands (in the day I mean) was way thicker than neccessary, and if you look in the tube, you see a very heavy seam. I think the thickness of the tubes is the real weight maker.

Steel comes in an infinite variety of alloys. There are significant differences between low carbon steel, high carbon, chromoly, mangaloy, etc. Butting the tubes seems to be specific to bicycles and really helps to shave off a few more ounces from where the tubes have too much metal. I'd say the stickers are a marketing ploy, but also a way to tell the consumer what they are getting.

To generalize, if the alloying metals increase the yield strength the tubes can be made thinner and withstand the same loads without failing as a thicker (heavier) tube set would. As they are thinner they are also more flexible, as alloying does not increase the stiffness of steel - the tube dimensions control that. Look around with Google and you'll find many places explaining this in greater detail.

Low end 'gas pipe' tubing is plain mild steel. Mid line tubes would be non-butted chromoly or manganese steels. A slight change in alloy and adding butting to these and you get Reynolds 531, Tange #1 etc .. As well, the mix of tubes in the frame made a difference in costs - full 531 stays and forks vs. plain mild steel could save a full pound or two from a frame. Bare frame and fork weight is a good indication of steel quality, as is the seat tube diameter.

THIS LINK (http://www.materialsengineer.com/E-Alloying-Steels.htm) helped me to understand the characteristics of different steel alloys.