scirocco wrote:I suspect that what happens is that they don't just pick tubing that is really thick and strong. Cost is everything with Ti, and to keep the cost down on the low end versions, they deliberately select a size down (in diameter and thickness) from the higher spec models. This is not quite thick enough to be really stiff where it needs to be, and it's not quite thin enough to save weight where you can get away with less stiffness. Kind of the worst of both worlds. But good enough to market as "the fantastic ride of titanium". (And it is).
To be fair, this may not be all that big an effect. Probably you get more stiffness from oversized bottom brackets and head tubes. And you don't get those on "budget" Ti, again, because that costs more than just welding straight gauge tubes together.
That doesn't play out this way when ordering a Ti frame from the big Chinese custom shops (XACD in my case).
Within reason, the customer is free to spec whatever tube spec they want, for no change in price. Straight-gauge only, of course (butted tubing is an extra cost, because the butting process is expensive), and restricted to standard tube sizes and thicknesses. I went for "standard" 38.1 x 0.9mm downtube, for example, but others have gone fatter (I've seen up to 50.8mm), and some people up the thickness to 1.2mm if they think they'll need it.
Things like integrated or tapered head tube cost more, I assume because they need to be machined out of a very thick chunk of material - which is expensive in both material and process.
Butting tubes gives a typical option of 0.9 - 0.6 - 0.9mm wall thickness. So you save 0.3mm thickness in the centre section (you need the thicker ends for weldability)... for whatever weight benefit that gives. My rough calcs say you'll drop about 15g off the downtube by going butted. Expensive way to shave weight, IMO.