KeithC2Turto

Looking at having a boll bar built for my C2 Turbo and have some questions.

Local club rulles say I can use alternate tubing sizes so long as they are as strong.

I am alowed EOM or DOM 1.75x.120.

Which is the weakest? If I go down a size to 1.5x.120 in the stronger, is it as strong as the weaker type in the 1.75x120.

If so, where can I find writen support incase I get a challange.

Is there anything in the SCCA rules about using the smaller size.

Chrome Moly seems to be out as the builder says it has to go out for heat treatment to mormilize it.

I want the smaller tube as it will be lighter and take up less room, expecially w padding.

Also, any picts of the factory 964/993 roll-cage rear sections out there?

Keith

RedlineMan

Hey;

I am not familiar with "EOM." It's a bicycle thing as far as I know. The two common types are DOM (Drawn Over Mandrel, or seamless) and ERW (Electric Resistance Welded or "electraweld"). I see nothing wrong with ERW at all, but SCCA has seen fit to ban it for new cages. I don't think PCA has any problem with it yet. As you were told, CR (chrome moly) is rarified stuff. If you could find someone who knew how to deal with it properly, they would charge a princely sum, you can bet!

Your car is a bit portly if it is stock, and unless you get real serious with plastic parts and hacking out steel, you will fall to the large-tube side of 2500lbs. You will be required to use 1.75x.120 for the three main hoops and the header in either DOM or ERW.

Here are a couple of examples I've done to get you in the mood!

KeithC2Turto

Nice!

It does say:

"seamless ERW or DOM"

and for over 2500# of 1.75x.120.

and, "an alternate diameter and wall thichness equal to or exceeding the bending strength of those specified"

Thus was hoping that 1.5x.120 DOM would be an acceptable alternitive to 1/75x.120 ERW.

Again, wow! I wish!!

Keith

What is HREW

RedlineMan

Who's rules are you reading here?

Or are you misquoting, as methinks? "Seamless ERW" is an oxymoronic statement. You can't have seamless welded tubing, eh?

The minimum standard in your weight group (2500+) for mild steel (DOM/ERW) is 1.75x.120 for the three main hoops and header. END OF STORY.

They do allow other materials such as CR (chrome moly), stainless or Iconel. These have a far higher strength-to-thickness ratio than mild steel, and if a wall thickness is chosen that matches the bending strength of mild steel, then these materials are allowed. You better be prerpared to back it up with ironclad SAE documentation. Obviously using thinner wall tube gives you a lighter cage with the same stiffness. Any good metal outlet you might choose should be able to provide you with the SAE specs for the strength of these various metals. Any high-tec fab shop will already know.

Having said all of that, forget it. Find someone who will do it in 1.75x.120 and go for it. Use DOM to maximize your rules compatability. K.I.S.S.

KeithC2Turto

Darn, you 'r right...

Geo

Actually, the SCCA sets size by weight. In the SCCA for you weight of car you could use 1.75 x 0.095 or 1.50 x 0.120 for both GT and IT categories. Not that your car would be IT legal.

Actually, that's apparently a common misconception. I read somewhere that even the FAA does not require special treatment for less than a certain thickness (0.250" IIRC). You may want to look into this. There is no welding standard for race car rollcages that I'm aware of, so the FAA standard should probably be sufficient.

Bill Gregory

FAA or FIA?

Geo

Federal Aviation Administration.

Aircraft standards are probably adequate and lacking a standard by a sanctioning body, it's probably the best we can do.

RedlineMan

Hey Guys;

The problem with CR is that it "can" require VERY specific treatment. The heat from the welding process (particularly MIG) causes the metal to become brittle, and if it is not annealed or stress relieved properly it can shatter like glass.

I myself do not know exactly under what circumstances this is a possibility, but for my own part I would make DAMN SURE I found somebody certified in metallurgy and/or welding to make sure the proper procedures were followed.

CR has definite advantages, but knowing its proper implementation is CRITICAL!
--------------------------------------------------------
FYI - PCA 04 rules for Roll Cage Tubing:

Cars over 2500lbs

Mild steel - 1.5x.120 or 1.75x.095
Alloy - 1.5x.095

Geo

Yep. That's why I mentioned the FAA quidelines. I think I heard about that on the Rennlist Racing mailing list if I'm not mistaken. Below a certain thickness the annealing is not required.