Framebuilders - OS tubes? or not?

OK, so for a typical lugged steel frame what might be the weight penalty of using a 28.6 top/seat tube, 31.7 down-versus the traditional 25.4 top, 28.6 seat/down tube when building the bike? Is it going to be that much stiffer? Assuming of course your using the same tubing for each scenario.

In building a 55cm cross bike for myself (145lbs) I can't quite convince myself that OS tubes will be necessary *regardless of how much cooler it looks :)

you can tell me I'm a ****** if you want, but just to let you know-I'm not that concerned with how much my bike weighs. Just a little curious. Or stupid....

Thanks

Standard sized tubes, like Columbus SL, are typicaly butted .9/.6mm, but OS tubes, like Columbus Zona, is .7/.5mm with shorter butts. At the end of the day, the OS tubed frame will be lighter, because the tubes are thinner (which saves more material than the larger diameter adds), AND slightly stiffer as well (by a small margin). One advantage to the thicker tubes is dent resistance.

Of course this is my opinion, but you might want to call Joe Bringheli for some Dedacciai ZeroUno tubes. They are OC tubes that come butted .8/.5 but with very short butts so there is not a lot of the thicker end left after trimming to size. A 55cm frame will build out under 4 lbs. and will ride very nicely for your purpose. Extra bonus is that Joe's prices are the best around.

Good luck.

Short butts+ lugs= Many not-so-good possible outcomes. Make sure you know the butt lengths/lug lengths are compatible.

OS tubes gives you significant gains in stiffness. However, in order to come in at the same weight, they have to be very thin. There's a crumpling effect at 50:1 diameter-to-wall-thickness ratio (think soda cans). So the tubes can be delicate as far as dent-resistant and have more catastrophic failure modes. I really like the tapered tubing that Serotta uses, makes a lot of sense to put the wider sections where the most stresses occur at the BB.

Short butts+ lugs= Many not-so-good possible outcomes. Make sure you know the butt lengths/lug lengths are compatible.

This is very true. Some tubesets like Dedacciai Zero (or now currently known as SAT 14.5) have very short butts and it's not possible to get the entire lug to fit on the butted section if building a frame smaller than about 55 cm. ZeroUno or Zona is no problem though, and most True Temper tubes are okay as well. Pay attention to what you are doing, and stay away from the killer thin stuff, and all is well.

I agree that butt length becomes an issue when building a lugged bike when heat isn't as localized as say fillet or tig. So stock tube length is pretty important. For now I'm going to try a standard tubeset, probably dedacciai com, with 8-6-8 walls. I know I'd notice an increase in stiffness with a thinner walled, os tubeset but it sounds like a task better taken on by a more experienced builder. Or maybe when I have some more money to throw at a frame.

thanks for the insight

oh yeah, fyi- I'm happy with sub 5lbs, let alone sub 4..

A ZeroUno OS tubeset is only going to cost about $30 more than ZeroTre. When you consider the major time investment you are going to make into building the frame, the money is insignificant. Also, fillet brazed is the least localized when it comes to heat application since it takes the most total heat (not the highest temperature).

I borrowed the Paternek fillet braze video. One thing that shocked me was how much brass was added to the frame to build the fillets. Almost seemed like the weight of slightly heavier tubing could have been accomodated for the reduction in weight that TIG might have brought.

I would check out the tubing reference on the Henry James site. You need the bigger tubing when the weights rise. As long as you are building for stick insects the light stuff rules. Even average weight riders relative to the general population, may fall off the charts.