going to finally put a 12 point cage in my dart is the weight savings of moly over mild worth the money also about how much weight saving would be expected

You will save about 30 to 40 lbs, but at 3 times the cost.

I cant quote prices but I doubt a CM cage is 3x or even 2x the cost of mild steel. Besides thre weight savings benefits, chromoly is much more desirable if you ever sell the car later.

I think a lot of chassis shops arent even doing MS anymore..

WOW, 3x the cost??? I don't think so! My Art Morrison cage kit is Chromo, and it wasn't near 3X more for it over mild. And that is just the price of the kit, the install is the same price or less even. The guy that installed my cage prefered chromo, since it is cleaner to work with. I saved the extra cost of the chromo in the price of fabrication.

My chromo "8 point" (it is a 10 point, Art Morrison doesn't count the D Bars) was $520. Same cage in MS is $285. They hadn't done an Aspen before, so they went and found one, and measured it up. It took two weeks to be build, AND shipped to me in Canada.

The shipping weight was 104lbs. This included the 6x6 mounting plates. The kit also came with a drivers door sill bar, and a dash bar, which I used for sub frame connectors. 2x3 would have been better I guess, but with a 10 point cage in the car, it is very stiff.

Going to a 12 point is going to make your front suspension work better too. My next car will have an Art Morrison 12 point ( or 10 point as they call it)

Here are some prices to go off of. Phone the actual chassis companies for this kind of info. I too thought a chromo cage would be way more than a MS unit.

http://www.artmorrison.com/2006cat/54.pdf

-Kenny

So, We all know the Chromo cage will be lighter, and numbers are always thrown out as to what the weight savings is. However I have never seen any actually calculations on it. Since today is Sunday, and I am bored, I figured I would nerd out, and do some math for fun.

I went out the the garage and pulled the tarp back on my 1967 Plymouth Valiant that is currently playing the role of my spare shelf holding up old clothes, empty boxes, etc. I roughly measured out the tubing that would be needed to make a 12 point cage in the car. I figure I would need about 740" of tubing.

I am going to abbreviate some of these down.

A1= Area of tubing using the outside diameter (OD) of the tubing.

A2=Area of tubing using the inside Diameter (ID) of the tubing.

AT =Area of total profile of tubing.

PI = 3.1416. PI is a mathematical constant whose value is the ratio of any circle's circumference to its diameter

R = Radius of a circle

Density of Mild Steel = .2833 lbs./in³

Density of Chromoly = .2833 lbs./in³

V = Volume

W= Weight

MILD STEEL ROLL CAGE TUBING

Roll cage tubing in MS is 1.625" in diameter, and has a wall thickness of .134".

OD = 1.625"

ID = 1.625-(2*.134")
= 1.357"

1. A1 = PI*R²
=(3.1416)(1.625/2)²
=(3.1416)(.8125)²
=(3.1416)(.660015625)
= 2.074in²

2. A2 = PI*R²
=(3.1416)(1.357/2)²
=(3.1416)(.6785)²
=(3.1416)(0.46036225)
= 1.446in²

3. AT =A1-A2
=2.074-1.446
= .628in²

4. V = AT * Length of tubing.
= .628in² * 1.00in
= .628in³

5. W = V * Density
= (.628in³)(.2833lbs./in³)
= .178lbs.

So, the weight of Mild Steel Roll Cage tubing is .178lbs. for every inch of tubing.

CHROMOLY ROLL CAGE TUBING

Roll cage tubing in chromo is 1.625" in diameter, and has a wall thickness of .083".

OD = 1.625"

ID = 1.625-(2*.083")
= 1.459"

1. A1 = PI*R²
=(3.1416)(1.625/2)²
=(3.1416)(.8125)²
=(3.1416)(.660015625)
= 2.074in²

2. A2 = PI*R²
=(3.1416)(1.459/2)²
=(3.1416)(.7295)²
=(3.1416)(0.5321705)
= 1.672in²

3. AT =A1-A2
=2.074-1.672
= .402in²

4. V = AT * Length of tubing.
= .402in² * 1.00in
= .402in³

5. W = V * Density
= (.402in³)(.2833lbs./in³)
= .114lbs.

So, the weight of Chromoly Roll Cage tubing is .114lbs. for every inch of tubing.

THIS WORKS OUT TO A 36% WEIGHT SAVINGS

SO, now that we know the weight per inch, how much is the weight difference between a MS roll cage, and a Chromoly Roll cage in the same car?

Let's Assume we will be using 740" of tubing in this example, based off of my Valiant.

Total weight using a mild steel cage = 740" * .178lbs.
This gives us 132lbs.

Total Weight using a Chromoly cage = 740" * .114lbs.

This gives us 84lbs.

Now, The 740" is a very rough measurement. I suggest you go out to your car, and do some measuring. Figure out how many inches your cage will be, then multiply that by .114lbs. for chromoly, and .178lbs. for Mild steel, and see what you come up with.

Please feel free to check my math too, I am human.

-Kenny

Cheap MS bar or cage, MIG welded is cheap. That's because welded tube is cheap DOM mild steel is almost as expensive as moly. I can definitely see how a 4130 Moly Bar that must be TIG welded can be 3 times the price. But its lighter, stronger and TIG welds look a lot nicer.

FWIW Mine is Moly. Do it once, and do it right.

Math looks good to me.

When I priced out tubing for my RoadRunner, it was almost double for CM over DOM. I know others will say it's bunk, but around here I could not find it any cheaper. Most steel places didn't even want to bother looking for it as it's not worth the time for a small amount. Most chassis shops buy in bulk at 2-3000 ft at a time. The 50# savings wasn't worth the extra money for ME. As far as resale, I don't sell anything so that wasn't a issue.

Jeff

This was brought up at the "For A-bodies Only" website also. I voiced my opinion there, but I think "jericogtx" pretty much explained most hobbyists view..........

Oh, the cost of the CM isn't what gets you. Locally it's the price to weld it! Most shops around here think they're welding titanium so they jack the price up accordingly. My shop literally DOUBLED the price of my cage 'cause I wanted CM. Sorry, for a dual purpose car I just can't justify the expense even if would have been only a few hundred bucks more.

When I did the cage in my 68 Dart I used MS DOM 1 5/8" x.134 wall. It was nearly $3 per ft. I bought the bender and bent all the tubes myself and then my son did the Mig welding because we didnt have a tig machine.
I cant tell you how much I have in the cage because we did ALL the labor.

I will never do a car in mild steel again the looks,weight,cert,and resale is a no brainer for me,but may not be right for every one.