TiHabanero

If comparing a 28.6 tube with a 9/6/9 butting to a 31.8 tube with 7/4/7 butting. the butted sections, and tube lengths are identical. Will the OS tube resist flex better than the standard heavy walled tube, or will the thinner walls negate the size advantage?

unterhausen

there are two bending moments that you have to consider. Bending and torsion. I'm too lazy to do these calculations. I have heard that 26.8 8/6/8 is equivalent to 31.8 7/4/7. I think that's in torsion, because that one's easier for people to focus on. But I switched from 9/6/9 standard dimension bike to 7/4/7 OS, and I didn't really feel much difference. So :shrug:

niknak

The OS tube will be ever so slightly stiffer in deflection and torsion and weigh a little less too.

TiHabanero

My understanding is torsion is a twisting motion, kind of like windup, and deflection is lateral movement across the tube diameter. Thank you for the input. Now I just have to figure out a way to explain this to someone.

Nessism

This is my understanding as well only the weight savings is noticeable. I ran calculations which confirmed this some time back.

79pmooney

Keep in mind the OS tubing (.6mm wall thickness vs 8mm for 26.8 tubing will be more dent prone based on both the thinner wall and less curvature. These will overshadow the stronger modern steel by quite a lot. (My 40 year old Mooney would have more than a few dents had it been built with the equivalent oversize tubing (had it existed). Also rust does far more damage to thin tubes as it basically reduces wall thickness.

I know this makes me look like a retro-grouch. Maybe but also an engineer.

Ben

unterhausen

your 40 y.o. bike is made from tubing that is pretty low-end from today's standards. Similar oversize tubing available today will not be 7/4/7, it's all 8/6/8 or thicker. Any steel bike should have rust treatment. My 7/4/7 bike saw some pretty rough treatment and never got any dents. About to get that frame back on the road after a seat tube replacement necessitated by a ham-handed attempt at removing a stuck seatpost.

I'm also an engineer. The difference between an engineer and a garage tinkerer is knowing where the limits are. 7/4/7 tubing has been shown to work pretty well over a long time period. Anyone can make things more stout and call it good. In fact, there is nothing wrong with that, but you don't need an engineer.

Nessism

Columbus performs some sort of surface hardness treatment on their tubes to make them more dent resistant. And personally, I'll take an OS frame over STD size 9/10 times.

unterhausen

I guess I wasn't paying attention, I didn't notice it when Columbus introduced the dent-resistant tubing. I saw the Columbus + tubes the last time I was looking for drawings to find butt lengths. I think Henry James is blowing out the non-+ tubing. You have to email them for a list.

I generally prefer standard size tubing, but OS works great. OS seems to be the sweet spot unless the tubing is going into a loaded touring or utility bike. 2OS just seems too heavy. I have a set that I just don't want to build into a frame.

Nessism

The 2OS lugged frame I finished last December weighed right at 4 lbs painted. Probably could have cut a few extra ounces but lightweight wasn't the focus.

unterhausen

I'll probably build it eventually. The tubes are really long too, so that increases the impression that they are heavy. The bike I bought it to replace is a real pig, must have 1.1mm wall tubes

Jmclay

When I performed this analysis a year or two ago the 747 31.8 came out to be 17% lighter and 1% more flexible than 969 28.6. The calculations included identical length butted ends and center section. The butts were simplified as a step located in the middle of the transition section. As mentioned above, the main/detailed analysis was for torsion but I performed a rough calc for simple bending to confirm that the torsion analysis was a reasonable proxy for both - it is. So the OS 747 is a tad lighter with not a whisker's difference in flexibility.

For 28.6 747 vs 25.4 969 the 28.6 was 16% lighter and 3% stiffer; again, a tad lighter and an insignificant diff in flexibility.

I use standard diameter tubes, generally 969 but sometimes 858. To me, the weight savings of thinner wall isn't worth whatever reduction in dent resistance or corrosion allowance accompanies it; not that I don't treat the ID of the tubes but I like knowing that if any rust develops in between rust prevention treatments then it has farther to travel before it's a problem.

As to going thin wall: I figure that if Jan's Pacific NW crew, who are doubtless much stronger than I, need 747 for best planing then I'd need 525 to get the benefit and that's not happening. So while I totally buy the potential benefit of strain energy as an aid to bicycle propulsion, it likely isn't terribly relevant to me. If I want to go faster then addressing the motor is the key, not the frame.

And as a general note: I find it interesting to have heard reports of OS 747 planing but not the same with conventional diameter tubes in 969. That strikes me as odd.

As another general note: Shortening the butted sections and lengthening the center section, will have a significant effect on flexibility.

unterhausen

I always wanted to try some of Jan's 7/4/7 standard size tubing, but never really had a reason to do that yet. They may be stronger than you (and me) but I'm not sure that they put more load on the bike. Batch of lightweights. I'm pretty sure I saw Jan in 2011 on PBP, he's not a particularly big guy. About like me if I lost 20 pounds.

Jmclay

PBP this year might help take care of that?!

unterhausen

unfortunately, I'm quite capable of keeping up my weight on a 1200km ride. I rode a 1000km brevet in June and didn't lose any weight at all.

TiHabanero

"unfortunately, I'm quite capable of keeping up my weight on a 1200km ride. I rode a 1000km brevet in June and didn't lose any weight at all."

Must be a member of the Clean Plate Club.

Was raised by depression era parents and we always ate everything on the plate. To waste food was to commit a sin. To this day, I still think about the Clean Plate Club from my childhood.

unterhausen

what's funny is I have trouble eating on longer rides. I waste a lot of food.

TiHabanero

On a ride this morning I was thinking about this and figured it is age related. I simply cannot lose weight unless I keep a hungry stomach at all times. If I do, then I don't sleep well at all.