Utility Cycling - Steel vs steel?

What are the pros and cons of Chrome moly steel versus High Tensile steel? I think for a bike frame High Tensile would be fine but I keep hearing about how chromo is the way to go. Why is that? If I back out of my driveway in my vehicle and run over my bike I think it would not matter what kind of steel is used if the bike is mangled. Thanks!

Oops I forgot to add that I'm thinking of getting a longtail bike soon if that even matters to this discussion.

Cro-mo has a very high strength to weight ratio, and is quite a bit tougher than standard "high tensile" steel.

Thus, manufacturers can build a much stronger bicycle of the same weight, a much lighter bicycle with the same strength, or strike a balance in between with a bicycle that is both somewhat lighter and stronger. It is simply a superior material.

http://en.wikipedia.org/wiki/Chromoly

Manufacturers can build extremely strong, long lasting frames from chromoly, then apply other engineering tactics such as butting the tubing and shaping tubing to increase weld area to create a strikingly tough, well designed frame.

These, along with other nice touches such as forged (rather than pressed) dropouts are touches which you will often see on a good cromoly frame, but much less commonly on high tensile. Cheap dropouts can be easily bent and damaged, as an example. There are other materials and methods in construction which can really improve the durability of a frame.

Overall, the bikes made with cromoly are simply generally nicer. Manufacturers typically aren't pairing good construction practices with poor materials. This is a general statement, but high quality techniques and design tend not to come on lower quality, lower priced bikes. You can find cheap cromoly frames without these nice touches, but even these frames still have the stronger steel at least.

High tensile is still an acceptable material to use on bicycles, it is on a great deal of vintage bicycles, and many low end bicycles today. It is simply heavier, can not be made as strong without needing excessive amounts of it, and the engineering touches added to these bikes weren't / aren't in compare with higher end models.

Abneycat;

Excellent and clear explanation.

I would add that historically probably 90%+ of steel bikes made in the world have been High Tensile steel or even lower grades. Historically Chrome Moly and other very high strength steels have been used only on higher end lightweight bikes, a relatively small part of total production.

[QUOTE=HPJeep;8477498If I back out of my driveway in my vehicle and run over my bike I think it would not matter what kind of steel is used if the bike is mangled. Thanks![/QUOTE]if the objective is running over the bike with a car and mangling it, your best bet is to go to the dump and get a pre-mangled bike. The reason that bikes made high tensile steel are heavier is that they are afraid it will fall apart at the joints. So they make it heavier

Abneycat, your post pretty much says it all about these two steels. Well done, mate!:thumb:

i can't find a reference now, but i distinctly remember my surprise upon learning years ago that chro-mo (4130) steels were only a few percent stronger (tensile, yield) than hi-ten aka carbon or 1020 steels. like 5% or less. so yes, chro-mo is better, but not to the high degree commonly implied. if shaving a pound off a piece of sporting equipment is worth a few hundred dollars, it is likely that you'll favor 4130: you'll find several sources of butted tubesets specific to common sport designs. if we're talking some utility rig that's likely to be pretty heavy anyway, or maybe a tandem, and of an unusual design not lending itself to off-the-shelf butted tubesets, hi-ten is perfectly serviceable.

we sell a lot of dutch utility bikes. they are heavy, hi-ten, well-made with forged dropouts and full lugs. many times people say things like "pity they don't use chro-moly!" implying that many pounds could thereby be saved. in fact, it would likely add a few hundred to the price and save 2% the weight.

I wonder then how much better the 853 steel is than regular Cro-mo (4130)?

i can't find a reference now, but i distinctly remember my surprise upon learning years ago that chro-mo (4130) steels were only a few percent stronger (tensile, yield) than hi-ten aka carbon or 1020 steels.


Your numbers are off, yield and ultimate are about 30% higher for 4130.
4130 is still a low-end steel relative to the better bike steels.

Maybe you were thinking of modulus of elasticity/Young's modulus. Alloying doesn't change this much. Thus cheap, heavy frames with the same size tubes are stiffer.


I wonder then how much better the 853 steel is than regular Cro-mo (4130)?
853 ultimate tensile strength: 1250 - 1450 MPa
4130 UTS: 560 MPa
1020 UTS: 395 MPa

Didn't find yield for 853, wondering if they alloyed the normal steel yielding behavior out of it.

if all this is true, why is my lht so goddamn heavy??

if all this is true, why is my lht so goddamn heavy??
they made it out of thick tubing. I'm trying to figure out why my Reynolds 531 bike is so heavy. I think it's the Brooks pro.

I'm pretty sure my 4130 bike is heavy because it was cheap.

I'm pretty sure my 4130 bike is heavy because it was cheap.

Yes, that can be one reason. At the lower price range, manufacturers can build bicycles using 4130, but skip out on some of the other good measures I mentioned, such as butting the tubing. They may also do other things, such as buying cheap stock of 4130 tubing despite it not being the "proper" tubing for the application.

Sometimes, on the low end 4130 is simply used as a "selling point" rather than a platform for a really great frame. Cut from the came cloth, but tailored into something different.

RE: LHT:
The LHT is built with heavier tubing than say, a racing bike, in order to retain proper strength and stiffness for loaded touring. It is also a mid-range bike, a great value and a great bike, but not quite up there with some higher end units. I believe higher end stuff is relegated to smaller scale, specialty production now. The Miyata 1000 was a nice bike.

The Surly Big Dummy longtail is 100% double butted cro-mo. I'm very pleased with it.

I'm pretty sure my 4130 bike is heavy because it was cheap.

...or was it cheap because it's heavy. ;)

Thanks Abneycat for the excellent info. So cromo is not only lighter but stiffer and resists bending more too? Basically just a stronger overall steel if the same gauge tubing of high tensile and cromo is used? I appreciate the input.

So cromo is not only lighter but stiffer and resists bending more too?

Lighter for the same strength. Essentially the same stiffness for a given cross section, so chrome-moly bikes tend to be LESS stiff than a Hi-Ten bike because there will be less steel (thinner walls or smaller tubing). Stiffness to road shocks is not a desireable frame trait...frame flexing absorbs some of the shock. Chrome moly is strong enough to take this flexing and spring back. Flexing also allows the stress to spread over a larger area, so not all the stress is concentrated at the joints. The thick steel in Hi-Ten frames tends to give them a "dead" feel, and the stiffness tends to cause them to fail at the joints.

Chrome moly is a bit more expensive material. The big difference is that Hi-ten can be welded with a few hours training and a MIG machine. It doesn't get hardened by the heat of welding, due to it's minimal carbon content. Welding chrome moly _properly_ requires a good deal of training and post treatment to stress relieve the joints. The alternative is brazing either with silver or bronze filler, which requires near perfect fitup and skill to do the fillets, or lugs, which add expense. In any case, Hi-ten is suited to mass production with minimally skilled labor, while Chrome-moly (done right) requires a trained craftsman. So the material increases the price a little, but it is the labor that really makes chrome-moly bikes cost so much more.

I dunno, but my 853 bike is light stuff -- surprisingly so.

It surprises people when they pick it up. They know I ride steel and so they think my ride is a pile of bricks -- until they give it a lift.