Point83.com

Googling "4130 vs 531" (which as lee notes is kinda funny) yields some interesting results, such as:



which has some good overall info on the meaning and various uses, and also links to some good other pages, such as:



which has some in-depth (neurotic) info on what grades are best suited to particular applications and even parts of a generic frame.

The numbers either refer to different brands or alloys. Sometimes they can also refer to wall thickness (for instance Ishiwata 022 is .9mm thick at the butts, Ishiwata 019 is .8mm thick at the butts).

It really doesn't matter than much. The stiffness of the tube doesn't change measurably with the alloy.

The tensile strength (basically how easily it dents is breaks does). That is important if you want to make really thin tubes. The vast majority of production steel bikes don't have really thick frame tubes.

The higher end (thinner) stuff is hardened. This increases tensile strength but makes the tubing more brittle (so cracks start and propogate more easily). Common brands that you'll see for hardened tubing are Reynolds 753, 853, True Temper OX Platinum, or Tange Prestige.

If the tubing is hardened but thick (like .9mm at the butts, .6mm in the center section) then it really has no advantage compared to unhardened tubing besides costing more. So usually it is used on race bikes where they want to use thinner tubing to save weight.

Tubing diameter makes much more a difference, but most people don't notice it. Until the late 80s/early 90s almost all steel road bikes (including loaded touring bikes) had 1" top tubes and 1 1/8" downtube and seat tubes. Now "oversized" tubing is so popular that it is the norm, and that is a 1 1/4" downtube and a 1 1/8" top tube and seat tube. An oversized .7/.4/.7 tube (considered thin to very thin) is about the same stiffness as the .9/.6/.9mm tubes found the classic road bikes and only very slightly lighter.

Surly uses both thick and oversized (or very oversized on the LHT) tubing which is much stiffer than anything that you'd find on older bikes. Great for controlling shimmy, not so great for the ride (in my opinion).

If you really want to get nerdy I can dig out my spreadsheet with deflection calculations for common tube sizes.

My frame that broke used small diamter and very thin hardened tubing (.7/.4/.7). It rode great, but the head on collision with a car started a tiny little crack (invisible after the crash) which now goes all the way around the downtube. A .9/.6/.9 downtube that wasn't hardened wouldn't have ridden as nicely, but probably would still be working.

alex

Oh, one more thing.

"Hi-Tensile" or "1018" tubes are pretty junky.

4130, 531, True Temper anything, Ishiwata 022, most Tange tubes are good.

Anything labelled as the generic "chromoly" is generally 4130.

apart from hi ten frames being heavy, would this material make any difference with how sustainable the BB threads are or how it does after a rain?