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Old 08-29-07, 04:34 PM   #1
.42.
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how can you tell Chrome moly from high tensile steel?

How can you tell Chrome moly from high tensile steel?

I'm considering buying a vintage bike and would of course like to get chrome moly if I can.
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Old 08-29-07, 05:05 PM   #2
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Can it even be told? A tubing sticker would be the giveaway

After that I think its just best guess based on weight. Maybe can make assumptions based on tubing wall thickness too
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Old 08-29-07, 05:08 PM   #3
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Lift it.
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Old 08-29-07, 05:32 PM   #4
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Isn't there a "ping" test?
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Old 08-29-07, 08:52 PM   #5
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Isn't there a "ping" test?
Yeah, it's called Rockwell or Brinell hardness testing - but you need specialized equipment.

Or you can look at the tubing label.
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Old 08-29-07, 10:11 PM   #6
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If it rides well, do you care?

Most often, cheap tubing got the short shift of workmanship and expense of fittings, stamped rather than forged dropouts etc.
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Old 08-29-07, 10:22 PM   #7
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Weight is a big deciding factor. I can usually tell by thumping the middle of a main frame tube with a fingernail. A butted chromoly frame will make a high pitched ding, while a High tensile non butted frame will usually make a dull thunk. Usually the finish work on a nicer bike will be better too. And yes, a tubing sticker works wonders too, lol.,,,,BD
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Old 08-29-07, 10:30 PM   #8
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Tap it...Listen feel. High ten tubing blows. Use the knuckles on the tubing, do you feel any spring? It should have some ring to it on your fingers. Look for a tubing decal. Look for ordinary sloppy lugwork. Look for cottered cranks. Look for dorky chainguard/spoke guards. High ten bikes are dime a dozen.
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Old 08-29-07, 10:39 PM   #9
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In my experience (51cm-56 cm lugged frames), a bare frame in Hi Tension steel can typically weigh seven pounds or more. Reynolds 531, Columbus SL, Chromor, Aelle are in the 4-5 pound range.
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Old 08-29-07, 10:49 PM   #10
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High ten bikes are dime a dozen.
hehehe, sellers on Craigslist seem to think otherwise....LMAO!!
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Old 08-29-07, 11:08 PM   #11
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So it should be generally heavier and more rigid, that's why it dings.

Thanks for the advice.
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Old 08-30-07, 04:10 AM   #12
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Gauss
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Old 08-30-07, 05:06 AM   #13
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So it should be generally heavier and more rigid, that's why it dings.

Thanks for the advice.
No, Hi-Ten is heavier and more rigid, that's why it thuds.
Chromoly is lighter, more flexible and dings when thumped.
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Old 08-30-07, 05:08 AM   #14
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Seems like CrMo would be more rigid and lighter. and high ten would be flexible and heavy.,,,,BD
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Old 08-30-07, 05:14 AM   #15
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Seems like CrMo would be more rigid and lighter. and high ten would be flexible and heavy.,,,,BD
Did I get it backwards? Maybe I'm confusing rigid with a more solid feel with Hi-Ten.
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Old 08-30-07, 05:53 AM   #16
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No, Hi-Ten is heavier and more rigid, that's why it thuds.
Chromoly is lighter, more flexible and dings when thumped.
Nope. Hi-ten and chromoly have pretty nearly the same density, and similar Young's modulus. A heavier wall tube is heavier and more rigid. A thinner wall tube is lighter & more flexible.

Now, hopefully you'll never run into a thin wall Hi-ten frame! However, there are a few chromoly straightwall frames out there that are pretty portly.

Bare piece of tube? In a materials lab you could check hardness as mentioned above, or pull a sample for UTS. In your home shop, you could give spark testing a go.

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Old 08-30-07, 06:01 AM   #17
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Or you could just not buy a bike that has been repainted and/or stickers removed. Plenty of them still around.,,,,BD
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Old 08-30-07, 06:10 AM   #18
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Now, hopefully you'll never run into a thin wall Hi-ten frame! However, there are a few chromoly straightwall frames out there that are pretty portly.
Now, what if you have a chromoly-stickered frame that doesn't say it's butted, but it's much* lighter than another frame that you know is straight chromoly. Could it be thin wall chromoly, and is there a problem with that similar to thin wall hi-ten?
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Old 08-30-07, 07:15 AM   #19
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I'm confused now. I guess it's down to workmanship and rigidity of the frame.
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Old 08-30-07, 07:19 AM   #20
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The most practical way to determine the tubing in an unmarked frame is via the seat post diameter. The lower the tensile strength of the tubing, the thicker the tube walls will be, resulting in a smaller seat post diameter. Typically, hi-tensile steel frames use seat posts under 26.0mm. Cr-Mo is generally 26.0 and over, with anything 26.8 and over generally being butted.

Of course there are some exceptions and doubts when you get a measurement that is in one of the crossover zones and the outcome does not necessarily apply to stays and forks, which were often downgraded from the main tubes, to save a few dollars. Last, this rule of thumb cannot be applied to frames with noin-standard sized frame tubes, such as many of the boom era French frames, which used undersized diameter tubing and have correspondingly smaller seat posts.
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Old 08-30-07, 07:26 AM   #21
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And Cinelli's (and a few other high end italians) use internal reinforcing at the seat lug, resulting in a columbus SL tubeset with a 26.4 seatpost.
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Old 08-30-07, 08:10 AM   #22
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If you rely on thumping the frame you might as well wave your hands around it and smell it

Kidding. Hi-ten tubes are generally straight gauge and thus heavier. I think it's softer (easier/cheaper to cut and braze)

I would follow T-mar's advice. Hints from the workmanship: thick, long, uncut lugs, stamped dropouts, sloppy brazing (blobs of brass around brazing area seen under the paint) indicate hi-ten. Components might give you a hint as well.
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Old 08-30-07, 11:15 AM   #23
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Nope. Hi-ten and chromoly have pretty nearly the same density, and similar Young's modulus. A heavier wall tube is heavier and more rigid. A thinner wall tube is lighter & more flexible.
Ok, we both said basically the same thing then. The heavier Hi-Ten has thicker walls making it more rigid.
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Old 08-30-07, 05:44 PM   #24
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The cheap high tensile steel wouldn't be as strong as an alloy, and while the walls are thicker, it still might not be as rigid...right? Depending on how much thicker it is, I guess...
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Old 08-30-07, 05:53 PM   #25
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The cheap high tensile steel wouldn't be as strong as an alloy, and while the walls are thicker, it still might not be as rigid...right? Depending on how much thicker it is, I guess...
Maybe we should go ask this in the Mechanics forum and see how big of a pissing contest they can get in over it? ROFL

(did i say that out loud?)

Last edited by McDave; 08-30-07 at 06:06 PM.
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