Plainsman

Question about frame building logic - is the decision to use single butted tubes vs double always driven by simple economy, or can their be solid design reasons for doing so? Noticed Giant alloy gravel bikes use single butted hydro formed tubes, while most other major mfgr gravel bikes use double butted tubes. I assume this decision was simply to save money in mass production, but wanted to ask. Is there a serious/appreciable weight difference between making a frame from double butted tubes vs single? A pound? 1/2, 1/4? TIA - just trying to learn!

guy153

Butting isn't just to save weight but to take stress away from the joints. It probably affects the feel of the ride as well. I don't know of a reason other than cost to only use single butting.

Trakhak

From what I just read in this review of Giant's aluminum grades, it seems more likely that Giant uses single-butted tubing in specific high-stress areas to increase strength. (By the way, I could be wrong, but I believe that every bike manufacturer uses a single-butted seat tube even when the top tube and down tube are double-butted tubes.)

I now know the answer to at least one bicycle-related trivia question: "What bicycle manufacturer smelts its own aluminum?"

dsaul

Its not always economy that drives single butted tube use. Sometimes, it just makes sense to use a thicker walled tube for dent resistance on an off road bike. You choose a tube with the wall thickness that you want and make it thicker at the head tube end, to minimize the risk of cracking at the head tube joint. The weight difference between double and single butted aluminum tubes is minimal.

unterhausen

I suppose if you are hydroforming a frame tube, some of this nomenclature loses a lot of its meaning. I have built frames with double butted seat tubes and try to avoid it if possible.

Nessism

This right here.

The Revolt 2 for example, has heavily shaped tubes. Terming these "butted" in any way is largely a misnomer. Most likely the forming operation begins with a single butted tube, but after forming a lot of the butt will be formed out.

pwyg

Single butted tubes are traditionally used as seat tubes. Since the introduction of Tig you now have bulge butt tubes to help support the swat area to reduce the chance of a fracture at the seat cluster area it is one of the highest stress areas inna frameset. Single butted tubes are thicker at the bottom where the extra strength is needed. For double butted tubes you get the thicknesses at each end to provide more strength at each of the joints with the weight savings of the thinner mid section. A straight gauge tube will be just as strong but a bit heavier. In reality the weight savings is not really a lot except for those who are convinced weight is connected to speed and therefor need to save every gram they can. The thinner mid section will also put a bit more compliance into a frame but again not a lot.

unterhausen

I think they might mean single butted in the same sense that fork blades and stays are single butted. They are thin at one end to start with and then get tapered down. So in the end they aren't too thick in the tapered section. In the case of the giant bikes, they are thick at one end and get hydroformed bigger.

Andrew R Stewart 

"Taper gauge" is a term that some frame tube companies have used to describe the before swaging down step. Andy