The Ugly Truth - Chrome Moly is NOT lighter than "regular" steel

[DesmoDog]

I apologize in advance for this post, it probably belongs in some other section if not in some other forum. But it's a pet peeve of mine going back to my motorycle days and I just ran across it numerous times while searching for other info and I have to vent.

We've all seen it. Search the web and nearly every bicycle site will tell you that chrome moly is some sort of lightweight steel. This is a lie. Any materials site will prove this out but the following is from https://material-properties.org/

Density of Chromoly Steel is 7850 kg/m3.
Density of High-Carbon Steel is 7850 kg/m3.

They have the same density. CHROME MOLY IS NO "LIGHTER" THAN CARBON STEEL. This isn't an opinion. It's not a secret. It's well documented.

Ok, put down the pitchforks. I'm saying the material isn't any lighter than carbon steel. The catch is, it is STRONGER, so you can use less of it (thinner tubes) and get the same strength. Chrome moly tubing is only lighter than carbon steel tubing if it has thinner walls so there is less material. And because chrome moly isn't much stiffer than carbon steel, that thinner wall tubing is less stiff than the carbon steel tube. This may or may not be a good thing, depending on your application. But it's something you have to consider.

So the bottom line is, sure, it makes a good material for bike frames, but not because it is lighter than carbon steel. It isn't. Frames made from it can be lighter because they can use thinner tubing IF they are designed to utilize the material's strengths. No pun intended.

Too long, didn't read version: Chrome moly is not lighter than carbon steel. It is stronger. Chrome moly parts are only lighter if they use less material than the carbon steel equivalent.

 

[MattiThundrrr]

You're not wrong. It is the butting that can be done to chromoly due to it's strength that makes the difference

Trust me, it is better

 

[horsefarmer]

"Frames made from it can be lighter because they can use thinner tubing IF they are designed to utilize the material's strengths."

I am lucky to have a few bikes made with cr-mo. They feel to me that the bikes have a springiness or torsion bar like feel built in without actual suspension components and very comfortable over bumps when road riding. Big difference riding same road with a Huffy mild steel bike.

 

[ifitsfreeitsforme]

good post. I have a couple "CR-MO" bikes that would serve as good boat anchors.

 

[MattiThundrrr]

IF they are designed to utilize the material's strengths

... and this is where the skills and knowledge of a master frame builder comes into play.

 

[Captain Awesome]

Hi ten
Cromo
Alum
Carbon

All have succumb to my influence under duress

No ti yet but hopefully I have a few more years in me

 

[ifitsfreeitsforme]

for some reason I have never wanted a ti frame.

 

[DesmoDog]

Oh man, don't get me started on titanium. I mean I love the stuff but it's also misunderstood.

Titanium is lighter than steel, roughly half it's density, but there are a lot of drawbacks. It's harder to machine, it's softer, it's more flexible, it's more involved to weld. But in general:

https://www.thomasnet.com/articles/...eel-vs-titanium-strength-properties-and-uses/

When comparing the tensile yield strengths of titanium and steel, an interesting fact occurs; steel is by-and-large stronger than titanium. This goes against the popular misconception that titanium is stronger than most other metals and shows the utility of steel over titanium. While titanium is only on par with steel in terms of strength, it does so at half the weight, which makes it one of the strongest metals per unit mass. However, steel is the go-to material when overall strength is the concern, as some of its alloys surpass all other metals in terms of yield strengths. Designers looking solely for strength should choose steel, but designers concerned with strength per unit mass should choose titanium.

Steel is real, baby!

I worked with titanium a little a lot of years ago and had some scrap I was saving for future projects. I was storing it at my mom's house. My dad was a shop teacher and it wasn't uncommon to have "scrap metal" around that he was saving for various projects.

Then one day I notice it's not there so I ask about it. She tells me she threw out all the scrap metal and will just buy me more if I need it. My dad had passed away a while before and she was finally cleaning up the shop... From the look on my face she knew something was up, but I just told her no, that's ok... she asked a few times what it was but I never told her. I had gotten it free and didn't really "need" it, so, whatever. I should have told her what it was when I left it there I guess.

Anyway... now that we've covered cromo and titanium, next we can talk about carbon fiber and they ways it gets misued!

 

[JA331]

I have 2 cr-mo bikes, a reissue kos and a late 80’s Shogun mtb. I can second the statement made by horsefarmer as to the springiness of both. The kos in particular is the one of best riding, reactive and fastest accelerating bikes I own in part I believe to its cr-mo frame and short chainstays. However the bike i own with the best ride is my aluminium framed Fast Ripper with 29” rims. I can only assume it must be due to the bigger wheels.

 

[Captain Awesome]

 

[MattiThundrrr]

View attachment 217873

That's going in the folder for later use. I predict it'll go over like a led zeppelin (ALSO EFFIN CARBON FIBER!!!) at the MTBRRR

 

[us56456712]

I apologize in advance for this post, it probably belongs in some other section if not in some other forum. But it's a pet peeve of mine going back to my motorycle days and I just ran across it numerous times while searching for other info and I have to vent.

We've all seen it. Search the web and nearly every bicycle site will tell you that chrome moly is some sort of lightweight steel. This is a lie. Any materials site will prove this out but the following is from https://material-properties.org/

Density of Chromoly Steel is 7850 kg/m3.
Density of High-Carbon Steel is 7850 kg/m3.

They have the same density. CHROME MOLY IS NO "LIGHTER" THAN CARBON STEEL. This isn't an opinion. It's not a secret. It's well documented.

Ok, put down the pitchforks. I'm saying the material isn't any lighter than carbon steel. The catch is, it is STRONGER, so you can use less of it (thinner tubes) and get the same strength. Chrome moly tubing is only lighter than carbon steel tubing if it has thinner walls so there is less material. And because chrome moly isn't much stiffer than carbon steel, that thinner wall tubing is less stiff than the carbon steel tube. This may or may not be a good thing, depending on your application. But it's something you have to consider.

So the bottom line is, sure, it makes a good material for bike frames, but not because it is lighter than carbon steel. It isn't. Frames made from it can be lighter because they can use thinner tubing IF they are designed to utilize the material's strengths. No pun intended.

Too long, didn't read version: Chrome moly is not lighter than carbon steel. It is stronger. Chrome moly parts are only lighter if they use less material than the carbon steel equivalent.

More expensive, harder to weld, harder to remove dents and harder to spread

 

[Ulu]

I’m trying to figure out if I’m gonna have an easier time TIG welding Cro-mo steel, silion-bronze TIG brazing, or just plain torch brazing.

 

[JA331]

The fabricator who built all the chromoly suspension pieces on my racecar always used a TIG welder.

 

[rickpaulos]

Hi ten
Cromo
Alum
Carbon

All have succumb to my influence under duress

No ti yet but hopefully I have a few more years in me

All have succumbed to my* influence under stress.

* Okay, not me but my friend Jeff. He has broken aluminum, carbon steel, cromo and titanium (twice). He knows better than to even try a carbon bike.

 

[rickpaulos]

I’m trying to figure out if I’m gonna have an easier time TIG welding Cro-mo steel, silion-bronze TIG brazing, or just plain torch brazing.

Some tubing manufacturers mix their steels specifically for certain types of welding.
Reynods 531 is a brass braze only (never weld that stuff) while Reynolds 853 was made for tig and pre-heat treated. Any new stuff will have specs that will say what type of welding technology is acceptable. You can always take the Schwinn approach, use thick walled material so it can withstand the most construction abuse.

 

[crumbling]

This is interesting as I own an early 1900 fixed speed road racing frame that the closest I can date it is 1916. The frame was made of steel tubing from Accles and Pollack of Birmingham and numbered as frame set 36. A&P appear to have a set number on the steering tube and also on the BB. The bare frame weighs 5 lb and bare forks 1lb 9oz. Accles and Pollack made large quantities of tubing for all uses from bedsteads, furniture, cycles, aircraft and cars. They made the first all steel tubed aircraft in 1913, but the design was a failure. They instigated the IT Group in Birmingham and bought Reynolds incorporating them to there holdings. Directly A&P stopped manufacturing cycle tubing and used Reynolds name. The A&P tubing was considered to be superior to Reynolds as it was Air cooled and it welded with a better result.
The tubing with my frame is butted seamed straight gauge with generally 25swg for the top and down tubes full length. The seat tube is 24swg. The tubing does not have manipulated wall tubing and is not Chromo steel. As you can see the frame is very light for a 1916 frame and does compare to the weight of early Reynolds tubing with manipulated wall thickness. The early manufacturing of steel tubing goes back to pre 1840 in the UK and USA where tube was initially manufactured by boring a small hole in bar steel then expanding the hole to what became a tube. Expensive but with no quality on the wall thickness. In the 1840`s the method came about to supply constant wall thickness tubing by milling flat steel sheet to a constant thin gauge and cutting it into strips and forming it to a tube that had butted edges that could be seamed by welding or fussing the steel or just left with a butted edge for steel conduit. This depended on the end use of the tubing but the process was called seam welded butt tubing or butted tubing.
The forks and rear stays are both tapered, the forks are also curved. The lugs and fittings are machined. The bars and front stem are the Major Taylor as A&P were licenced to make. The sales drawing of frame sets is similar to what I have but the sketch is dated 1922.
An A&P stamping appears on the steerer tube along with a number 36. The steel is noted to be A&P A grade. I have seen other A&P frames that have a similar stamping.
These are the British standard wire gauges converted to mm. As you can see the higher the SWG number the thinner the metal.

24 SWG = 0.022” / 0.559 mm

25 SWG = 0.020” / 0.508 mm

The problem of weight was solved by A&P by using thinner walled tubing were they could.

Crumbling

 

[Ulu]

What I am working with is that Centurion Tange bicycle, Which is evidently double butted. The fact is that I don’t care about weight much, and I could add a triple butt if I like.

Anyhow, I can experiment with it a little bit, but I thought I should ask questions here first before I torch.

I have been dying to try the silicon bronze TIG, But the truth is that I am the most adept with oxy-acetylene torch by a good margin.

I will admit that I learned a lot when I TIG’d the Mongoose. I will be a lot better at it the next go round.

 

[Kevin B]

DesmoDog, You started a good thread. Thanks, this is very informative. There are some great replies too.

 

[MattiThundrrr]

This is pretty cool, a catalog of all the Tange products, including diagrams and descriptions of the various types of butted tubing

https://velobase.com/CatalogScans/Tange_1988.pdf