Regarding butted tubing, here's an interesting old pre-Blug blog post I saved long ago. Not sure if it exists still (it does <http://rivbike.tumblr.com/newsarchive>!). Some earlier thoughts from Riv/Grant on straight gauge tubing.
Best, joe broach pdx or The T:T Faqtor?March 23, 2010 It’s the Tube-to-Tire Ratio Factor. Friend Ted wrote a couple of days ago and as part of a long email that included family stuff and a video, he also out of the blue said something like, “fat tires and skinny frame tubes look way better than skinny tire and fat frame tubes.” I’d already been working on that exact topic, and it was reaffirming to hear Ted say it right there out of the blue. I wonder how many other people have thought the same thing. The early mountain bikes were great, widespread examples, but it doesn’t have to be that extreme to look good. (A current Atlantis-Bomba-Hunqa with fatties is the same). There’s no formula, so I’ll make it up on the spot. It’s not a formula to be taken too seriously, it’s just for fun and to get you to think about it. And it is truly loads of fun. The skinniest tire on the bike should be at least 11 percent larger in diameter than the average diameter of the seat-, top-, and down tubes, and at least 16 percent larger than the front-to-back dimension of the fork. You add the diameters of the three tubes. Divide by three. Multiply by 1.11, and that’s your visual minimum. For the fork, measure front-to back and multiply by 1.16. Maybe the calculated tire size won’t fit. The formula isn’t designed to make your frame or fork look bad. It’s designed to make your bike look good. Whether it still rolls or not is another issue, but fat tires + skinny frames and forks = hubba hubba. The seat stays and chain stays are sad to be left out, but there’s a formula there waiting for somebody else to come up with. Bicycle looks, or aesthetics, are not the most important topic in the world of bikes, but they’re always at least in the background, and I don’t think anybody can deny that they care how their own bike or bikes look. It doesn’t matter to me what you like, and shouldn’t matter to you what I like, but Ted and I like the same look, it seems. In bicycle frames, I guess what we’re talking about is the “lead pipe look” of inch or inch-and-an-eighth top tubes, inch-and-and-eighth seat tubes, and inch-and-an-eighth to inch-anda-quarter downtubes … especially when combined with 32mm or larger tires, which make the tubes look even skinnier. We don’t make frames out of lead pipes, or anything close. A thick tube has a wall thickness, at the end, of just 1.0mm (1/25.4th of an inch). For most of their length, the tubes in our frames average about 0.7mm (about 1/36th of an inch). So no, not lead pipes, but the lead-pipe look. Big diff there. (Not more tea; more tea flavor. Remember that one? Lipton has what—-just given up? Commercials now are cars and drugs and sodas, with now and then a fast-food.) Maybe you have to be old to like the skinny-tube look. For sure, the bikes I grew up with had skinnier tubes still. Schwinn Varsities, for instance, —- I’m sure they had top tubes that were less than an inch in diameter. (Unrelated but noteworthy, their fork blades still hold the most aerodynamic of all time record.) Those Varsities had the skinny-fat thing going on. Those bikes were nearly indestructable, and maybe living with them, and old Raleighs, Peugeots, and Motobecanes that basically never died is why I associate skinny tubes with strength. I know the physic-al advantages of fatter-thinner tubes. More torsional rigidity and lateral stiffness per ounce, but that comes at the cost of dent-resistance and toughness. Beer cans dent easily, and V-8 cans from the early ’70s don’t (didn’t). Putting more metal between the air outside the tube and the air inside it makes a tube harder to crack or buckle. There’s a balance between weight, strength, efficiency, durability, costs, and marketability, but there’s not one tiny sweet spot that gives you the best of everything. It’s always a compromise. Usually the compromises err on the side of marketability, because sales drive everything, and there are some smart battles that a manufacturer could spend a lot of money fighting, with no chance of success. For instance, a good case can be made for straight-gauge (not butted) top tubes and down tubes. A straight-gauge top tube is less likely to dent in a crash, and weighs only about 2.5 ounces more. That it costs less makes it seem worse, but I’d say it’s better. We use butted tubes on most of our bikes, although the Bombadil and the big Homers have straight gauge top tubes—as they should. A straight gauge down tube resists twisting more, and down tubes are supposed to be heavier than the other tubes. Here again, it would weigh about 2.5 to 3.5 ounces more, and you can lose that much fat in a day easily (not that you want or need to!). -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
