Nice essay, Dave, and very helpful. My concern on the thinwall tubing starts at the factory -- and may end there. True seamless tubing is made by forcing a ram through a billet, and then rolling things out. I've never seen (or looked for) a study on tolerances in wall thickness. With the successive rolling exercises, it would be easy for a 0.4 nominal wall to be a 0.3 on one side and a 0.4 on the other. Unless the factory has x-rayed (or ??? as equivalent), I'm uncomfortable with a really thin wall. The reason I'm uncomfortable is that thinner tubing walls are more likely to fail by buckling, not just dimpling. So, I'd love to try something else, but for now I stick with good old 531, 4130 in all its permutations, and 6061-T6 (aluminum).
harvey sachs mclean va
At 08:16 AM 10/17/2000 -0700, dave bohm wrote:
>Hi Jerry and Everybody,
>
>Metallurgy and tubing design is a very complicated subject. Not one we
>can adequately cover in this forum. I can clarify a few questions though.
>
> > Heat-treated or no, I think 753 and other thin-walled tubeset are just too
> > thin. The simple fact may be that 531 or maybe 531SL along with Columbus
> > SL represented the best compromise between lightness and durability. What
> > we have seen since is tubes that are made too thin, then hardened in some
> > way to try to compensate for being too thin in the first place. I'm not
> > convinced that there has been any real metallurgical advance which has
> > really allowed a lower weight than 531 or Columbus SL without some
> > undesirable tradeoff.
>
>There have been significant advances in the materials used in bicycle
>tubing since 531. The extra strength of modern materials has allowed the
>tubes to be thinned slightly and still retain adequate strength and
>longevity. Other improvements in materials allow for less damage to the
>tube after brazing or welding. I don't know if I believe that air
>hardening tubes are actually a benefit in bike frames but they are not
>hardened before use. They are of a class of air hardened tool steels (A2
>etc.) that harden after being heated to a critical temperature (which
>varies depending on the alloy).
>
>, it is less because of technical advances than because the public
>is willing to accept them as a throway item like modern aluminum frames, to
>be used 2 or 3 seasons, then discarded.
>
>It is true that some of the very newest tubing, i.e. Foco, Ultra foco,
>Zero, EOM 16 are so light that they have sacrificed longevity. I too
>disagree with this trend. Eventually I hope to see a backlash from the
>consumer. The butting profile on Ultra-Foco is .56-.36-.56, EOM 16 is
>.6-.3 (it tapers down) for example.
>Many thin tubesets have proven themselves to be very reliable. Columbus
>El has been around for quite awhile now and at 7-5-7 works
>great. Prestige was very reliable tubing and quite thin. Modern
>offerings from True-Temper at 7-4-7 have proven to be extremely reliable
>also. I built a BMX jumping bike for a friend of mine out of Platinum and
>It is still holding up great after nearly two years. I can guarantee this
>bike has seen more abuse than any road bike would see in a lifetime.
>
>With the proliferation of tubesets recently, I'm not
>even sure which ones have adopted the thin wall throwaway approach and
>which if any may have a wall thickness comparable to 531 or Columbus SL.
>Tubing and frame ads don't typically list wall thickness. Anyone know of a
>listing of wall thickness for most of the current tubesets?
>
>I need to reiterate that tubing is pretty far down on my list of
>importance when building a bike frame. The stiffness of a tube is
>dependent only on its diameter and thickness, not the specific material
>its made from (as long as you're comparing steels). Almost all the tubing
>from the different manufactures is of very high quality and will make
>excellent bike frames that will last a very long time.
>
>Sincerely,
>David Bohm
>Bohemian Bicycles
>http://www.bohemianbicycles.com