I'm with Jim M. that rifling in Columbus tubes is a marketing gimmick. In the steerers, and in SLX/SPX, the rifling is so slight that it can't hurt much. In fact, it does add a bit of strength and stiffness, just not quite as much as the same amount of material would if evenly distributed around the tube.
One can show mathematically that it must be so (well, I can't, but I had to derive the proof as an exercise in engineering school - it's freshman level stuff, that I forgot right after the final exam!) Basically, the farther the metal is away from the central axis of a tube, the more it contributes to stiffness and strength, so you don't want anything projecting inward closer to the axis. Columbus ribs don't project inward much, so it's not a big deal either way.
They did screw up when they went to TLX though, IMHO. (I hope TLX isn't off topic; I don't know what year it came out.) TLX is rifled the whole length of the tube, unlike SLX/SPX which are rifled only at the ends. The main problem is, they decreased the butt differential from .9/.6 to .8/.6, presumably because it's harder to get that rifled mandrel out after butting. An .8/.6 tube is weaker than a .9/.6 tube where it counts, where almost all frames bend/break - in the butt - but not much lighter, since most of the length (and weight) of the tube is in the unbutted section. Compared to an .8/.5 tube with the same strength, the .8/.6 tube is a good bit heavier.
An even higher butt differential than .9/.6 would be advantageous, at least at one end. 1.0/.6/.9 or .9/.5/.8 triple butted for instance makes a lot of sense for toptube and downtube, with the heavier butt at the headtube end. .8/.6 was just a step backward no matter how you look at it, and it was made necessary by the decision to rifle the full length of the tube. So rifling per se isn't so bad in moderation, but watch out for what else might come along for the ride.
Lou Deeter wrote:
> Jim Merz and others, what do you think about Francisco Cuevas
> putting the X in the steerer tube? Did that strengthen the tube more
> than the rifling or was that just his way of marking his bikes?
For pure bending, where the bending is in only one plane, an I-beam is better than a tube. A thin-wall tube is the most efficient shape for resisting bending that can come from any direction. Steerer bending stresses are mostly fore-aft, but with a lateral component that may be significant, I don't know. Is a tube with a plate down the middle a good hybrid between a tube and an I-beam? I doubt it. No numbers to prove it, but I'd bet money that Cuevas's steerer is weaker than one the same weight that is just a tube with the extra metal put into the wall thickness. The Cuevas has too much metal right down the middle where it's not pulling its weight.
Mark Bulgier
Seattle, Wa
USA