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.
