Peter Carroll/Toronto

Actually, many of these international cages would not pass our North American rules. Not they they are necessarily bad, but they are based on a different approach to safety.

I was looking at the new Rahal Letterman M3 GTR at the Glen last fall with the guy who designed my cage. He pointed out some features that would not qualify for BMW Club Racing.

For example, there was no cross member behind the driver. Instead the space was open and the belts had to stretch all the way to the back seat. In North America you generally must have a cross member and they prefer the belts attached to it. These are completely opposite views.

Also, the tubes making up the main hoop were all straight pieces welded in cluster joints. In NA they generally want bent tubing all in one piece.

From example, the BMW CCA Rule Book says:

3. Main Hoop
A. The main roll cage hoop shall be as wide as the full width of the interior and must be as close to the roof as possible without violating the provisions of “Inspection” outlined below. One continuous length of roll bar tubing shall be used as the main hoop. The main hoop must consist of not more than four (4) bends maximum, totaling one hundred eighty (180) degrees +/- ten (10) degrees and in the same plane.

4. Diagonal Brace
A. At least one (1) diagonal brace shall be used in the same plane as the main hoop. One end of the diagonal brace shall attach to the corner, or horizontal part, of the main hoop above the driver’s head, within twelve (12) inches of the driver’s-side corner. The other end of the diagonal brace shall attach to the mounting plate (or to the main hoop as close to the mounting plate as practically possible) diagonally opposed to the driver’s head (passenger floor).

So by these standards, one of the word's newest and most advanced race cars would not even qualify for BMW Club Racing.

Don't even get me going on the seat back brace... Apparently the BMW factory doesn't want your seat anywhere near the cage.

Interesting. Don't you think?

DWalker

Most rule books actually read that it has to eet their minimums OR you must submit the engineering data behind why your cage is the way it is and then prove that it meets or exceeds their crash protection standards

flatsics

I like cage pics.

Jeff Lamb

The first two and the last three pics posted by flatsics appear to show a couple of different versions of the "geometric X" for the door bars.

The 911 cage shown in the first two pics shows the geometric X with the short center tube running down to the sill tube. The enhancements to this design would be to add the sheet metal tacos at the point of the X and to possibly tie the sill tube into the chassis sill where the short center tube meets it.

The (944 Turbo?) cage shows the geometric X with the sheet metal tacos, however, there is no sill tube.

What do guys think of using the lower sill tube vs not using it?

I am still trying to find an engineer within my company who can run some FEA modeling for me. Assuming I can find one, I look forward to posting some of the results.

Jeff

PogueMoHone

[QUOTE Interesting. Don't you think?[/QUOTE]

I have no expertise, particular knowledge, or dog in the hunt; and therefore no opinion or vested interest in the proper or correct answer.

I am just along for the ride, hoping to pick up valuable knowledge.

Thanks for your insights.

fatbillybob

I'm a sill tube fan unless the chassis has a huge rail like the outer hydroformed rails on say a C5/6 corvette which can be integrated into a cage to be a sill tube member. IMO the sill tube is important because it provided the lateral anchor to be the seat cage area where you can anchor the seat to the cage. The sill tube also lends support to the lower portion of the cage and supports the "x" to some degree as another triangulated structure. The problem of course is more weight. Somewhere around 2lbs/ft adds up very quickly.

Larry Herman

Yeah, but if it's at the sill tube, it's nice and low!