Out of curiosity, about how much weight can you expect a NASA legal cage to weigh, specifically for HC. I tried searching but came up empty handed.

 

That all depends on the cage builder, and what features you want incorporated in the cage...
To get a round about or a general figure is futile until you know what kind of features you want in it.
Searching would of done you little good here on that question.
Better to contact your cage builder on this matter.

 

Here, you can do the math. Depends on how much (length) tubing you use, what the thickness is, and the diameter of the tubes:

.095" thickness, 1.5" diameter = 1.426lb. per foot

.120 thickness, 1.5" diameter= 1.679lb. per foot

.120 thickness, 1.75 diameter= 2.089lbs. per foot

 

It depends on a lot of factors. I have done many different style cages and the weight was a factor in some and others it wasn't. You can do the basic math and get a pretty good idea. Figure 75-100ft of material. I did a CRX cage last year that needed some extra weight in the back of the chassis so I used some significantly heavier tubing in the rear reinforcements. I used thinner tubing up in the front.

On my GT3 car, I will be using every trick in the book to keep the weight down and yet to maximize the chassis stiffness. There will be at least three different sizes of tube, the minimum size material for the baseplates, and other reinforcement gussets, etc.

It all depends on your class. If you have to carry the ballast in a certain place, like the passenger floor board, why not build the lower portions of the cage out of significantly heavier material? Put the weight where it will do some good.

 

I think I used around 110 ft of tubing by Meris numbers should be close or a little over 200 lbs with plates and boxes. NASA legal and certified

 

Chromoly is lighter...

 

Chromoly is no lighter than regular steel (when using the same size material). SCCA and NASA both changed their rules for the tin tops. You are not allowed to run a thinner wall smaller diameter tubing if you run Chromoly vs mild steel. So you will save no extra weight. One of the benefits of Chromoly is, consistency. Usually its wall thickness is more uniform than even DOM. Plus it is has better quality control as far as the material. It is usually "cleaner" than mild steel although it really isn't an issue.

 

And the process to build a cage in chromoly is way more expensive since its more involved.

 

The process actually isn't all that much more expensive than a regular TIG welded cage. TIG welding is much more labor intensive than MIG, no stronger, just takes a lot more time. A properly built cage will take some time anyways. You will spend quite a bit of time prepping all the weld joints and the tubing fit up. Too many clowns out there just rough mitre or grind the tube intersections and goober some weld on there. Not even the same class as a properly built cage.

 

The op asked about weight. Not cost.

 

There are things you have to do to weld chromoly that you don't have to do for mild steel. For example, you have to pre heat the metal before you weld it or it will break the first time it suffers an impact.

And yes, it's lighter than mild steel.

 

You do not have to pre-heat thin tubular sections. The thicknesses we are dealing with are considered thin. If you use the proper rod you do not have to do a post weld annealing. If you use a 4130 rod to weld it you will have to bake the whole structure to normalize the weld zone. If you weld it with an ER70 or ER80-S2 rod you do not need to anneal the welds. You can gas weld chromoly very nicely. It has been done for decades in the airplane industry.

Mild steel and chromoly Alloy tubing are the exact same weight. They are both steel there is no difference in the weight. A piece of tubing 1.75x.095 will weigh 1.67lbs regardless of whether it is mild or chromoly.

Years ago, Chromoly was allowed to run one "size" smaller, thus generating a weight savings of course at more than double the cost.

 

Very educational

 

great info, very much appreciated

 

Owned <shrug>