Chrome-moly vs mild steel for cage

[Doug1]

Approximately how much weight savings would there be in a 10 point cage with swing out door bars when comparing chrome-moly to mild steel? This would be in a 2nd gen f-body.

I have a car that will get a LOT of carbon fiber parts and am thinking that I am giving away the weight savings if I go mild steel on the cage.

[go-fish]

You're opening up a big can of worms asking that question here. I was looking just last night, using the search function, about bolt-in cages/weld-in cages/ roll bars/ viability.....It quickly turned to this very debate you are asking about.

With my experience reading through 5 pages of the materials debate I realized it would be far more conclusive just to call a reputable cage builder with verifiable experience in the classes and racing organizations in which you want to run. You will get both sides of the argument here, both bring up good points, thins even get heated!

As far as safety equipment goes, I wont pose any questions on Pro-Touring.com. I'll go directly to a vendor, and several of them. Safety topics seem to be a point of great debate around here. Not to the point of anyone advocating un-safe practices or equipment but the employment of and methodology/theoryld of materials.

Some things are better handled when you're face to face with a pro.

[Bryce]

Johnny is correct. THe following is an example and you need to check the rule book to see what size tubing you need to use for your intended racing.

lets use 1.75" tube and lets say you use 50 feet to do a 10 point cage.

Mild steel has a .120" wall thickness therefore has a volume of 368.4 in^3, density of steel is .284lbs/in^3; total weight is 105 lbs
Chromoly has a .083" wall thickness therefore has a volume of 260.4 in^3, density of steel is .284lbs/in^3; total weight is 74 lbs

[exwestracer]

Be careful with that... SOME sanctioning bodies allow thinner wall tubing for 4130 material. Others do not specify material, only size and wall. In that case there is actually a weight gain with 4130. Also, 4130 is much more easily damaged by overheating during the welding process. Unless you are a good TIG welder, you're probably better off saying with mild steel.

If you are not building to any particular set of competition rules, you will probably be safe with 1 1/2"X.065 wall (4130) tubing gusseted directly to the body structure. In that case, the weight savings are significant.

[wmhjr]

Be careful with that... SOME sanctioning bodies allow thinner wall tubing for 4130 material. Others do not specify material, only size and wall. In that case there is actually a weight gain with 4130. Also, 4130 is much more easily damaged by overheating during the welding process. Unless you are a good TIG welder, you're probably better off saying with mild steel.

If you are not building to any particular set of competition rules, you will probably be safe with 1 1/2"X.065 wall (4130) tubing gusseted directly to the body structure. In that case, the weight savings are significant.

+1

Different sanctioning bodies often have different requirements. You need a good chassis builder and knowledge of exactly how and where you plan to use the build in order to come up with your answers.

[parsonsj]

As far as safety equipment goes, I wont pose any questions on Pro-Touring.com. I'll go directly to a vendor, and several of them. Safety topics seem to be a point of great debate around here. Not to the point of anyone advocating un-safe practices or equipment but the employment of and methodology/theoryld of materials.

Some things are better handled when you're face to face with a pro.So.. you're saying you'll only get one opinion when you go to several professionals, and you'll get many when you ask on an open forum?

I agree with the latter... but not with the former.

[parsonsj]

If you are not building to any particular set of competition rules, you will probably be safe with 1 1/2"X.065 wall (4130) tubing gusseted directly to the body structure. In that case, the weight savings are significant.I agree that that would probably be safe, and that it would save a lot of weight.

But I wouldn't do that, and here's why: most sanctioning bodies require 1.63 or 1.75 tubing of various wall thicknesses. If you show up at the tech station with 1.5 tube, you'll be immediately disqualified -- it'll be obvious. I would recommend one use 1.75 x .083 tube. It can be bent with most benders, and can at least pass the tube diameter requirements of most (though not all) sanctioning bodies. And it's lighter than 1.75 x .120 wall DOM, which seems to be the basic standard of heavier cars.

Anyway, just one opinion on an open forum. :)

[SShep71]

Doug, Two things:

More important than all of the numbers,weights, and measurements that so many people loose in the process is the fact that chromoly is not a "beginner" friendly material. It requires experience and more specific machines to work than traditional DOM mild steel. If you intend to do the cage yourself and are not familiar with the 40_ _ series tubing then its easy, mild steel. Don't allow the "WOW" factor or the maybe 100lb weight saving compromise for unreliability of a bad final product. Just like Johhny said go to a experienced fab shop that does 40 series and not just one what will ""Do"" 40 series. Im not suggesting that you dont know what your doing but the next guy that gets this idea and reads this thread may not.

Now in order to determine the weight saving you have to calculate the cubic footage of the entire assembly taking everything into account (tubes,crossbars,gussets,mouting plates,etc) of both types of tubes and do the math. You may have a different design between the two types of tubing because of the limits on the mechanical capabilities and the yield properties of the tube. (i.e. chromoly may require more gussets and bars than steel) but that is the way to actually determine the total weight savings.