How can you tell if a frame is chromo?

[John in CR]

Is there any sure way to tell if a frame is made of chromoly 4130 steel? I have the opportunity to buy some lightweight road bike frames made of 1" OD steel. Is this sure to be good steel or is there any chance it's the cheap stuff? Is there any sure way to tell, a scratch test, some marking somewhere on the tubing?

 

[LI-ghtcycle]

Do you know what brand/year/make the frames are? The only way I would know to find that out is to look up the bike on Bikepedia:

http://www.bikepedia.com/

As long as it's not too oddball of a brand or older than about *Edit* 1993 (or newer), you should be able to look up all that info and it gives you those kinds of details.

If it is steel and a premium brand bike and hella light, I would say it's a dead ringer for CroMo.

 

[vanilla ice]

There has got to be some way to test.. hasn't there. But I don't know how either so I go by the stickers and the weight. The extras added into the steel, I'm guessing you need some acid or some thing that would react to those things?

 

[LI-ghtcycle]

I'll ask my neighbor, he's welder by profession, he might know a rule of thumb, maybe something along the lines of taking a softer metal like say brass or aluminum and scratching the metal, and comparing the ease of scratching if you have two examples of each laying around, and obviously the milder steel will scratch easier?

 

[kriskros]

tryy Wicks aircraft supply... thet specialize in aircraft 4031 chromo.. check their wall thickness specs agains tr yours... that might help

 

[vanilla ice]

Is chromoly less magnetic than hi tensile steel?

 

[liveforphysics]

It's going to be very hard to tell.

I can't think of any simple way. If it's a quality brand of a quality bike and it's steel, it's almost certainly cromo though.

 

[dennyt]

If stickers exist, they can help:
Hi-Ten = high tensile steel, 1020
"Chromoly / 4130 Main Triangle" = the rear end is 1020
Reynolds 531, etc etc is all great stuff

If it has a bolt-on derailleur hanger plate (instead of an integrated hanger as part of the dropout), it's cheap steel.

Most high-end steel road bikes use very thin gauge, internally butted tubing. You might be able to tell by flicking the tube with your fingernail, or even squeezing it.

 

[Zoot Katz]

Spark Testing might be able to help you determine what's what.
Compare the grinder sparks with known materials.

 

[dogman dan]

My best guess, if they still exist, is to look at the components on the bikes. If the derailurs and brakes look wallbike, it's not going to be cromoly. If on the other hand, you start seeing good quality stuff, then likely the bike frame was too. If they were light roadbikes, like 25-28 pounds, then they will be good stuff. If heavy, then likely not.

 

[mrzed]

It might not help much, but back in the late 80's when I worked at a bike shop, the old mechanic showed me how to check the quality of the tubes by flicking a fingernail at them. Chromoly tends to be thinner wall, and more rigid, both combine to give it a brighter and longer ringing sound.

But the only way to learn this is by walking around a few dozen bike frames and listening for the subtle differences, especially as other factors will also affect the sound. Generally speaking though, standard hi tensile steel has a duller ring.

 

[Joseph C.]

It might not help much, but back in the late 80's when I worked at a bike shop, the old mechanic showed me how to check the quality of the tubes by flicking a fingernail at them. Chromoly tends to be thinner wall, and more rigid, both combine to give it a brighter and longer ringing sound.

But the only way to learn this is by walking around a few dozen bike frames and listening for the subtle differences, especially as other factors will also affect the sound. Generally speaking though, standard hi tensile steel has a duller ring.

This will make Beast very happy.

 

[MadRhino]

The only sure way to identify the grade of any alloy, is to send a sample to a metallurgy laboratory. They will need very little of it, and the analysis possibly free in some universities. The simplest test is to measure hardness (Rockwell) and compare with density (weight per volume). There are many other tests of course, the most precise implies atomic count, for that will give you the exact percentage of every elements.

 

[LI-ghtcycle]

The most important question is still unanswered!

Did you get the frames? What did you find out about them?

Pics!!

 

[John in CR]

The most important question is still unanswered!
Did you get the frames? What did you find out about them?
Pics!!

No, not yet. I'm just trying to arm myself with good info before visiting one of my LBS haunts that still has a decent size stack of frames left over from a container of old bikes he split with someone. I know he has some steel road frames, so I'll look for badges and stickers, along with name brands, derailleur hangers, weight and other info. My goal is to come away with a few to use for the good steel to use for lugs and parts, along with one complete frame with 1" OD tubing to complete a built on battery ebike idea.

 

[jateureka]

Checking the seat tube diameter might give you some idea, check this link http://www.bikeforums.net/archive/index.php/t-338383.html

 

[dogman dan]

If they are not too sun damaged, I think the majority of ones that are good chromoly will sport a badge saying so. Once you find one so marked, I think you will be able to put that one in one hand, and pick up others going yup, yup, nope. The cheap bike will be thicker wall tube and noticeably heavier. That, plus the components will let you know. Having a derailur hanger or not may be a real real good indicator. The cheap stuff will all have the horizontal dropout for the derailur with built in hanger.

 

[Drunkskunk]

mrzed alrecomended checking the sound. I learned the same method, and regular mild steel will have a duller tone.

You can look down the seet tube or anywhere there is exposed metal. Some types of Chromo can actuualy rust, but it doesn't look like regular steel. a mild steel frame will turn brown inside, like an old antique gun barrel. Chromo may have some rust, but it won't be even, and likely will still show bare bright metal.

Chromo is usualy brazed not welded. when it is welded, it almost always is going to be tig welded, so the diffrence is easy to spot.