mxt_77

I'm reading through the SCCA GCR section regarding rollcages (Section 9.4). It breaks down the required tubing size based on car weight, where one weight class is 3001-4000lbs and the one below it is 2201-3000.

For ITR-B, the S2000 is listed w/ a required weight of 3005lbs.
Section 9.4.1.F.4 states:
[QUOTE]For purposes of determining tubing sizes, the vehicle weight is as raced without fuel and driver. The minus tolerance for wall thickness should not be less than .010

Ludedude

The most common tubing size for cages is 1.75" dia x0.120" wall if you're using conventional DOM mild steel.

cthree

You answered your own question. 3005 - 180 < 3001 therefore 1.625"x0.120" or 1.75"x0.090" DOM tubing. You should choose the smallest OD tubing you can get away with. If you went with cro-moly it would be smaller still (a better choice if you can do it).

mxt_77

Another question/clarification. In the SCCA GCR, it states that the tubing size requirements for various car-weights and classes. For the 2001-3000lb range, they list the following:
1.500 x .120 DOM / Seamless / Alloy
1.625 x .120 DOM / Seamless / Alloy
1.750 x .095 DOM / Seamless / Alloy

Does that mean I can use any of those tubing sizes, regardless of whether I use DOM mild steel or chromoly? From what I've found, the 1.75x.095 is actually lighter per linear foot than the smaller diameter sizes with the thicker walls.

Orthonormal

The 1.75x0.095 would be 8% lighter than the 1.5x0.120 assuming the dimensions were exact.

mxt_77

Looks about right to me. The site I looked at had them listed as follows:
Chromoly 1.500" x .120" = 1.7690 lbs/ft
Chromoly 1.625" x .120" = 1.9200 lbs/ft
Chromoly 1.750" x .095" = 1.6790 lbs/ft

FormulaRedline

Actually, the 1.500" x .120" would be about 5% heavier than the 1.750" x .095" (which agrees with the lbs/ft numbers just posted).

If weight was the only consideration, that's a significant difference, but when welding a roll cage into an existing car, packaging is also a major concern. Make sure you consider this before you go out and buy one size just because it's lighter.

mxt_77

^ Yeah, good point regarding packaging. I got the same tip from a guy in my local forum.

krazik

Also check the weight of DOM, it should be about the same as chromo.

mxt_77

Yeah, same guy from my local forum just pointed that out, as well. Not sure why I thought chromoly was lighter. I think I'd just always heard that chromoly cages can be lighter, but didn't realize that it was due to the fact they can use smaller/less tubing and still have the same strength as mild steel.