To all:

Of the 3 resources of welding a frame composed of the same diameter and butted material let's say 853 for a standard for this question! I'm establishing a standard guideline to try to eliminate all variables.

Ok here goes: Weld 3 frames of the same material and size, but weld one by TIG, the other by Fillet Brazing, the other by Lugs! Of all which do you feel will be the most responsive and react to input from rider and trail conditions?

My opinions would be TIG with the heat hardens the area adjacent to the weld and stiffens the frame a bit in that area. Fillet Brazing doesn't have the heat but the overlap of the braze might stiffen the frame at the joint a bit. Lugs with the least heat and shortest area would provide a frame with more flex by the weld. I know there are many shapes of Lugs I'm taking the shortest ones. We have all seen frames broke adjacent to the lug so we know it stresses in that area. Of course it could be caused by the lip of the lug creating a stress forced leverage.

I look forward to your responses. Thanks...

All steel has basically the same elasticity so the lug frame would feel stiffer because it has a little more material at the joint assuming the lug is stronger than the tube.

Now if you were doing destructive testing, the frame with the least amount of heat-treat loss would bend the least. The lug frame would probably win here too if it is not over-heated. Annealing from too much heat reduces the yield strength of the tube.

I have ridden a gazillion bikes built a gazillion different ways, including a few with identical tubes and different joining techniques. You cannot tell by riding them. I'm sure there is some measureable (in a lab) difference in frame flex, but it's not worth worrying about. All of these methods work great to build a bike frame. One is not objectively "better" than the others.

-Walt

To all:

Of the 3 resources of welding a frame composed of the same diameter and butted material let's say 853 for a standard for this question! I'm establishing a standard guideline to try to eliminate all variables.

Ok here goes: Weld 3 frames of the same material and size, but weld one by TIG, the other by Fillet Brazing, the other by Lugs! Of all which do you feel will be the most responsive and react to input from rider and trail conditions?

My opinions would be TIG with the heat hardens the area adjacent to the weld and stiffens the frame a bit in that area. Fillet Brazing doesn't have the heat but the overlap of the braze might stiffen the frame at the joint a bit. Lugs with the least heat and shortest area would provide a frame with more flex by the weld. I know there are many shapes of Lugs I'm taking the shortest ones. We have all seen frames broke adjacent to the lug so we know it stresses in that area. Of course it could be caused by the lip of the lug creating a stress forced leverage.

I look forward to your responses. Thanks...
What's the question again?

853 is an air hardening alloy. Different rules apply though from what I can tell from your post, it still doesn't make a difference. Both tig & fillet brazing will take 853 above its transition temperature and induce hardening. This is not a bad thing as it increase the mechanical properties of the materials as it's designed to do. Brazing with lugs with brass will have the same effect. Brazing lugs with silver shouldn't take 853 above its transition temperature so you see no increase in its mechanical properties. Built to the same mass, they'll each be equally strong. To say a lug frame would be stronger may be true but it will also be heavier, so again, built to the same mass, they'll be equally strong.

You'd never, ever, ever, not even on your most princess and the pea day, be able to tell the difference in ride characteristics between identical bikes who's only difference is their joinery technique.

Am I correct in presuming that 853 tubing for bicycles are likely thin, less than 1mm?

Lugs would act as significant stress risers at small concentrated areas with little thickness, would they not?

By the way, I'm not a builder and don't know anything about welding...

Even plain 4130 tube is air hardening, it was designed that way so that aircraft fuselages could be welded and not lose any strength in the process. All these claims from tubing companies that their "special" material is air hardening is nothing special actually.

I agree, you would never be able to tell by riding which is stiffer; you would only be able to measure in a lab. In theory, the longest tubes would flex the most. Since lugs or large fillets shorten the tube, they should be slightly stiffer.