Wednesday, December 12, 2007

notes on tubing choices - you asked for it!




o.k., here ya'll go. i'll try to make sense here. the main design parameters by which tubing is chosen for a specific rider are, and this is the short list, mind you - are rider size {height, weight, body type: tall and skinny, short legs/long arms, visa-versa} intent {touring, mtb, cyclo-x, commuting} history {I've broken everything i own, i've had the same bike for years} and, just plain old bike size. allot of other factors are in the mix, of course, like what it's like where you ride, physiological characteristics, past and present injuries, personal preferences, age, and aesthetics.for instance, if you want a 29er with a 80/100mm travel fork, you have about 3 tube choices for the down tube - a heavy mettle dt, a true temper dt, or 4130 aircraft cromo that comes in 8' sticks. i usually choose the true temper 1.5" dt, as i like the thickness {.9/.6/.9, in mm's} and because the yield strength {the point at which a tube bends to a point at which it does not bend back, i.e., it is bent} and the ultimate tensile strength {it busts} are higher then the others. and, the butts are long {the thicker parts at the end which resist bending, and dissipate heat during joining} allowing use on a wider range of designs. also, as a rider get bigger, the butts get thicker, the outside diameter gets larger, and the actual thickness of the tubing profiles increases. one important thing to keep in mind which people often do not know is that ALL STEELS HAVE THE SAME DENSITY. if you take a 1.25" piece of prestige and a 1.25" piece of 4130 with the same diameters and thicknesses THEY WILL RIDE EXACTLY THE SAME. the differences are in the diameters, butting, tube length and shape. certain alloys impart differences in hardness, ductility, yield strength, and tensile strength, but not "ride quality". often, ESPECIALLY with alloys such as reynolds 853, THE ONLY TUBE IN THE BIKE THAT IS 853 IS THE ONE WITH THE STICKER. they don't even MAKE 853 seat stays and chain stays. have i confused everyone yet? sooooo...... basically, i choose my tube sets out of whatever company makes the specific tube i consider to be appropriate to the design which i have chosen. i like true temper toptubes and down tubes for mtb's. they have long butts for better resilience against suspension fork stresses, although for smaller riders, i have been using prestige, but not for much longer - i only have 4 dt's left, and it hasn't been produced since 1994. but, when those are gone, i'll just use appropriate true temper tubes. i just liked the prestige butting profile better. i use mostly dedacciai chainstays because they aren't too thin, and the bends are all in the right places. i use alot of nova seat tubes because they take a 27.2 seatpost, have long butts on the bottombracket end, and are externally butted, to which i add my external lug for added strength. i bend my own seatstays out of 4130 because it bends easily {if a one-ton arbor press is considered "easy!}and i use true temper headtube because it comes in long sticks that i can cut custom lengths out of it with out wasteful cut-off end pieces, and it's good and thick - i hate wallowed out headtubes! so, as you see, it's not as easy as saying "i want a 289.xyz frame" tubing choice is critical, and i try to optimise every design, even though it means getting tubing from four different vendors in ohio, california, and tennesee. if you want to know more, i would highly suggest reading scot nicol's 5-part metallergy series at the ibis cycles website, or of checking out where alot of framebuilders hang out and talk about this stuff, www.frameforum.net did any of this help, or just cloud the waters? and of course none of this has anything to do with frame geometry..... that will be another post. it's even more complicated! steve.

9 comments:

Preskit Matt said...

Heeheehee......sounds like you have a pretty good handle on your art, Steve! Thanks for taking the time to 'splain things.

Stay warm!

Preskit Matt

Preskit Matt said...

"As a rider gets bigger, then butt gets thicker".

Ain't THAT the understatement of the year! I'm goin' riding.....

PM

Sabrosa Cycles said...

"the differences are in the diameters, butting, tube length and shape"
you nailed it. it is all about the moment of inertia of the tube. There is a lot of hype about how different materials ride - but you get it.
nice.
I really liked the 853 comment too.

Japhy rider said...

clear as mud. the same density statement is interesting.

say, what does it mean for steel to be air hardened?

geek out,
McD

Anonymous said...

"THE ONLY TUBE IN THE BIKE THAT IS 853 IS THE ONE WITH THE STICKER"

What bike is this referencing? All 853's or just your own?
I've never seen more than one 853 sticker per frame.
Seems unlikely that only one 853 tube is allowed per frame?
Makes near-perfect sense to use 853 in the seat tube and the down tube.

swiggman said...

Howdy, Steve. Nice post...pretty much the best tube-choice dissection I have ever read. It beats the Rivendell version ( no offense to the good folks at Rivendell, keepers of the retro flame) and I'm sure I couldn't have put it so plainly, you almost have a Will Rogers style. Dang, you'll have to do a seminar at the NAHBS now ! By the way, a long time ago they used to make 853 chainstays...I think I even got some MTB versions from you. They weren't nearly as nice as Tange. A guy just cracked one on a 29er I built but it was a 6-7" rider and I was asleep at the torch the day I brazed in the left side dropout. Hey, nobody's perfect ! Cheers, Paul.

mimbres man said...

Oi Steve!
That was a great read. I’m interested in your take on geometry because that's where the rubber meets the trail. My two mtn bikes, though both are super nice Ti frames, have completely different ride characteristics I think mainly due to geometry.

Thanks for the primer on steel. I am looking forward on your take on geometry, i.e., racing vs. touring vs. expedition.

Do you think the arched top-tube helps with the ride or just looks bad-ass and is distinctively Coconino.

Interesting stuff indeed.
MM

Aki said...

Good writing, Steve!

I'm not a specialist for bike steel tubes, but ALL STEELS HAVE THE SAME DENSITY is the good point to mention steel's nature. (Do you remember I work for Japanese steel company?) .

I think downtube is the most important. The long butts is nice for me because some of my friends' bikes made with colombus or deda DT seems little lame at short point butts. Yes, I'm biased and it's because ride styles difference but I like the long butts indeed.

-Aki

steve garro said...

nice replies! we got two framebuilders, a guy in steel munufacturing, a science teacher a research bioligist, a nurse and a disgruntled anonymous guy collectively from japan, venezuela, california, nevada, utah, arizona and somewhere anonymous. like i said, read that scou nicol metal series.....i do about once a year to see how much of it has soaked in through use! steve.