DWalker

NASA also allows the use of ERW tubing, which is wrong. There is no arguement for it other than cost.
The idea that requiring the same size tubing in 4130 as DOM is stricter is flawed, it simply removes one more thing a tech inspector needs be concerned with. SCCA at least acknowledges the differences in materials.
A GT/Production, Formula, and Sports Racer class car is expected to be a proper race car and properly engineered, must be homolgated, and meets stricter requirements than a street car with a cage.

NASA basically copied the SCCA rulebook with the exception of making certian "allowances" so customers- which is what you all people participating in a for-profit event- could run cars they could not run elsewhere.

Yes, thier personal safety equipment rules are a bit higher, but they allow H&N restraint systems the SCCA does not, in keeping with thier "just get out there" mentality.

The SCCA has its flaws too, in that they typically are a bit slow to make some changes, but all in all there is a reason NASA chose to copy thier rule book (down to the illustrations )

95ONE

From the PCA rule Book Page 24;

Minimum Roll Cage Tubing Sizes
All required tubing must have the following minimum diameters and wall thicknesses:
Car Weight without Driver
Under 2500 lbs Over 2500 lbs
Mild Steel 1.50" x .095" 1.75" x .095” or 1.50" x .120”
Alloy Steel 1.375 x .095" 1.50" x .095"


But NASA's rules do dictate One size for mild steel or alloy.

Bryan Watts

Yeah, I pointed out as much in my two posts preceding yours.

Bryan Watts

They allow grandfathering of cars with a rulebook before 4/30/03. SCCA does the same thing for cars registered before 1/1/03. I don't see a huge difference there. They both allow cars built and registered prior to the 2003 season to run with ERW tubing.

It seems obvious that the SCCA rules would be a starting point for NASA, as they are the oldest game in town. NASA has taken SCCA's safety rules and improved on them.

NASA requires a SFI certified device just like BMW CCA, SCCA Pro, Grand-Am, NASCAR, etc. How is that allowing H&N restraint systems that SCCA doesn't? SCCA doesn't even require one. If anything, SCCA "allows" more devices even though they don't require them. I know SCCA racers wearing the non SFI approved ISAAC device.

It's actually opposite of what you suggest. SCCA allows any H&N device but doesn't require one. Here is the mention in the SCCA GCR:
"The use of a head and neck support system is highly recommended."

I suspect that has less to do with SCCA and more to do with Joe Marko being the safety advisor for most of these club racing groups, as well as NASCAR and the IRL. The truth of the matter is, NASA has stricter safety requirements than SCCA and is more of a leader right now in promoting newer safety technologies. BMW CCA, because of a close relationship with Joe, is even further along the curve.

TT Surgeon

CM is my vote. Might want to consider having one of the local circle track shops do the work for you. they typically do great custom work and won't charge you a p car tax.

Bryan Watts

I don't mean to be so contrary, but I very VERY much recommend against taking this path unless you know the shop has turned out some road racing cars and you've seen the work first hand. Without a few examples that you've seen with your own eyes (and preferably gotten some feedback on from others), I wouldn't dream of dropping a car off at a circle track shop and asking for a PCA or NASA legal cage.

I've seen more than a few cages come out of really good circle track shops that just don't meet the rules of SCCA, NASA, BMW CCA, etc because the shop simply doesn't know anything about road racing cages in unibody cars. Over the last 4-5 years, I can think of a few local cages that had to be cut out and redone because someone went down this path. From things like two piece diagonals in the main roll hoop when a one piece is required, all the way to using the wrong mounting points for the main 6 mounting points. I've seen curved rear down bars come out of circle track shops that also do drag racing work.

The cages also usually lack triangulation and proper nodes with load paths. It's no fault of the shop...it's just a different way of doing things. There's a lot more to building a good cage within a unibody than cutting some tube and being a good welder. A cage in a unibody not only needs to be there to protect the driver, but a lot of thought should go into mounting points, load paths, tiangulation, etc to result in the best performing car as well. Why have just a safe cage when you can have a safe cage that also increases the rigidity of your chassis?

I don't understand the obsession with CM for a club racing car. For a Pro car where you get hit a lot and may be rebuilding the car in 7 days between races, the stronger CM may make sense. For club racing, I would go with mild steel because it's cheaper and easier to work with. For the savings in material, you can afford to have additional bars and gussets added to result in a safer cage and more rigid unibody (for better performance).

IIRC, the amount of deflection when a force is applied is very similar for mild steel and CM. The difference is that CM undergoes plastic deformation (i.e. permanent bending ) at about a 20% higher force, so it's more durable for a car that gets hit a lot...which SHOULD be a non issue for most club cars. I'd rather spend the extra money on additional gussets or tie-ins to suspension mounting points than on the added cost of CM.

95ONE

I'm going to have to fully agree with you there. I thought / noticed the same thing when I read the CCR rule book on cages. They just took simplest from the SCCA and copied and pasted. Total lack of imagination here. But, other side of the coin type thing. SCCA has it's issues.

mark kibort

I was just busting your chops as you were me!

Hey, good stuff here. the more I look at my cage, the more it scares me!

next time, no cutting corners.

mk

DWalker

Agreed, although to be honest, most circle track guys give more thought to the car getting hit and protecting the driver than anything else, whereas "road race" shops tend to be so concerned with making the car stiffer and less concerned with driver safety than they should be.


Actually, The reason to go to 4130 tubing IMHO is simply save a bit of weight if your building a new "all-out" car. It doesnt make much sense to me at all to put a 4130 cage in a heavy, partially stripped street car with numbers on the side, but if thats your preference then have at it, just have someone who knows what they are doing fabricate it for you.

Bryan_H

Did NASA really intend to say that the bends should be mandrel bent? That would weaken the tubing. Shurely they ment DOM tubing?

BH

Bryan Watts

I'm not sure where there is much "room" for imagination. The cage rules of any organization in the US, whether Pro or Amatuer, read essentially the same because they have essentially the same requirements and they are all advised by essentially the same experts. And the basic requirements have essentially been the same for a pretty long time. If you've got a set of rules that is clear and accomplishes the goal, what point would there be in changing the wording around?

To be honest, after taking a look at the PCA rulebook, they could stand to do a little copy/pasting themselves. The wording in the SCCA rules is far more clear and detailed.

Bryan Watts

And the weight savings is even a moot point because many rule sets no longer allow you to use smaller/lighter tubing when using CM over mild.

The durability argument definitely makes sense for a Pro car and is the biggest reason I've heard for using it from folks who build pro cars. If I were building a car for World Challenge or Koni Challenge, I'd build with CM because durability is important and budget doesn't matter as much. If I were building a car for PCA or NASA, mild steel for sure, using the cost difference between the two materials to add additional structure to the cage to make it safer/stiffer.

Bryan Watts

I think you're confusing terms. They absolutely require DOM tubing. And they require the tubes be mandrel bent, rather than crush bent (as does every other organization whether they specify it that way or not). Bending always weakens the tubing...a mandrel bend weakens the tubing much less than a crush bend.

Crush bend on top. Mandrel bend on the bottom.



SCCA uses the following wording to make the same point:
"One (1) continuous length of tubing shall be used for the main
hoop member with smooth continuous bends and no evidence
of crimping or wall failure."

That's essentially the definition of a mandrel bend.

mark kibort

Correct!

So, SCCA limits tubing for cages to be 1.75 x .095, regardless of material . PCA does not. Sure, BMWCCA requires HANS, and SCCA doesnt, but the cars are as safe or safer in SCCA because of it. sure, some small differences as well, like 2 year old window nets, passenger side nets, and other small changes, but over all they are all pretty safety oriented. You can take your porsche from PCA and get sent home with a PCA rules based cage at an SCCA event, and I wont be able to compete with NASA until my window net is replaced. (or a BMW race until I get a HANS and a passenger side window net). I cant race in POC without a fuel cell, but I can in PCA or ITE SCCA. (but not SP). Lots of "different" rules sets.

MK

RedlineMan

Depends;

If you are speaking of linear compression strength of a tube, then yes, obviously. Nobody makes curved jack handles or home foundation supports. If you are meaning material strength, not necessarily. If the bends are of an unecessarily tight a radius (like the ones you showed), then you are likely correct. In this case, the mandrel bend probably does improve strength over the shoe-bent tube. The shoe bent tube will have excess stretching on the outside of the radius, and perhaps some buckling on the inside. If a more proper radius is used (7"+), this will be reduced to neglidgeable. The inside of the radius will likely be strengthened on both bends because of "work hardening." Then too, certain materials will work harden more than others.

In other words, excepting linear compression strength, I don't think you can make a blanket statement that all bends weaken the material intself.

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Anyone thinking of using a NASCAR or NHRA shop for cage work REALLY REALLY REALLY needs to follow your advice. I've seen the problems you mention too. Some of their ideas are absolutely confounding!