Cm vs Ms

12 point cage. What is the weight savings?
No i don't want a debate of whats better?
Matt

Significant on a 12 pt. Roughly, I think C/M is 30% lighter than M/S.

This is all C/M except for 2x3 rails. With the engine and rear axle out of it, I can flip the chassis around on the floor by myself.

Pounds per foot

1.675x.134 ERW 2.134
1.625x.120 DOM 1.929
1.625x.083 CMY 1.367

IMO in a 10/12 point typical 8.50 cert cage you will likely see a 30-35lb weight savings with moly over mild steel. I think many people go Mild for cost reasons. The material is less money and in some places easier to come buy and also can be mig welded. Which means less fitment time and a lower cost. I know you didn't want that but for a typical 8.50 cage it is not a ton of weight but in racing weight is weight

I'm anal about weight. Beyond that ERW is not good unless you're building a swing set. DOM and CM have been pretty close in price. 100' of CM is 56# lighter than the same DOM, and 77# lighter than the ERW. Value of the car is higher. And IMO is a better car.

Definitely way better resale

I was shocked when they handed me the main hoop with one hand...and it had the cross bar taped to it.

I had no idea it was that dramatic of a weight savings.

Thx for the info guys.
Matt

If I remember correctly when we cut the M.S. 12 point cage out of my buddies G Body (GM) & did the 25.5 cert C.M. cage upgrade when all said & done it was 25-28 lbs lighter than the old cage.

Basically the same thing we have found depending on the car being done. Thus my 30-35 guesstimate

So, how many more feet of CM tube did you use over the 10 point?

Any truth that CM joints need to be "stress relieved"? Read this many many years ago.
If true, how is it done?

My understanding its all about the cool down time.
In a perfect world yes it would be best to have it stress relieved.
I'm going with DOM 1020. For ME it's cheaper and easier.
Matt

Not in thicknesses typically used in race cars. Proper TIG techniques to keep the heat affected area to a minimum and getting tight fits at joints is needed though.

As per Lincoln Electric:
Q. Do I need to heat treat (stress relieve) 4130 after welding?
A. Thin wall tubing normally does not require stress relief. For parts thicker than .120", stress-relieving is recommended and 1,100ºF is the optimum temperature for tubing applications. An Oxy/Acetylene torch with neutral flame can be used. It should be oscillated to avoid hot spots.

I thought I heard somewhere about 500 years ago that at some point, C/M tubing became available annealed and that stopped the need for stress relieving. Since then all C/M tubing is annealed.

4130 tubing is available in different conditions. SFI specs call for Condition N or normalized for anything used in the structure of a chassis. Sheet is also available in Condition A or annealed which is not as strong and easier to form. There is also a hardened material that was talked about a number of years ago after some well publicized problems but hasn't been talked about for awhile.

Years ago I saw a car that wrecked hard, came apart and hurt the guy pretty bad. Nothing was bent, everything that came apart looked like broken glass. And this was not a backyard car. You have to pay attention to this stuff and where it comes from.

I remember the same thing but I think that was way back when NHRA allowed any type welding of C.M.
I don't think that is needed with Tig welding as already mentioned
Airplanes C.M. fuselages used to be welded with Oxy Acetylene gas welding a long time ago, I'm sure they needed it also

I like the idea and might anneal my tubing, how far out from the joint should this be done?

Chrome moly if welded with 70 S2 filler will not form a carbon line.

Some folks weld with 4130 filler. This produces a carbon line a couple inches from joint.

It best to keep welding area warm with cage warm. This reduces flash temperature. And do not cool welds.

Every broken tube Ive ever seen was welded with hard filler rod. They all broke in carbon line. If welded correctly you can bend into a pretzel and not crack.