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SCCA rules for roll cages, etc.
I am an SCCA tech inspector that has seen some VERY bad welds. First, in the SCCA General Competition Rules (GCR) the roll cage tubing size is determined by the car weight and class. In the case of Spec Miata the minimum size is 1.5 x .095 DOM tubing- NO ERW. These rules take bends into account. The bends must be a minimum of three times the diameter of the pipe. The number of attachment points is determined by the car class, in my case STU is limited to eight. The maximum area of attachment plate in all planes is 144 sq. in. and the maximum thickness this year is 1/4 in. (After several SM's put 1 in. plate in the right rear to get better corner weights.)
Wall thickness can now be measured with an ultrasonic thickness tester BUT, as was mentioned, it can be difficult to use properly. If the wall thickness is measured by drilling a hole make sure the bit does not strike the far wall as that will make the measurement too thin. Maximum hole size is 1/4 in., 3/16 in. preferred and anything smaller will not accept the depth rod of the caliper.
Second, all points mentioned about practice are good. In my case practice doesn't seem to help and I will have a professional welder do all the welds except for the attachment plates. I would definitely recommend building the cage but having a professional welder do all the tubing joints. If possible get a tech inspector to recommend a welder because not all road race car shops have good welders. If a car builder insists on welding his own cage I recommend going to a Community College welding program. He should also cut apart his practice joints to check for penetration, etc.
Gussets have not been mentioned but I highly recommend them. My car will have the maximum number of gussets per joint allowed which is two (SM is also two but other classes have no limits). Also any number of braces are allowed as long as they attach to only the attachment plates or the cage tubing and triangulation really helps.
Finally, what ever competition you are in be sure and get the rules, read them and ask questions before doing something that might have to be undone. If you ever think that you might change classes or sanctioning bodies try to prepare the car so that you don't have to tear every thing out and start over. We had a lawyer that thought he could do his own thing and found out that he couldn't change the rules to suit him.
John Cooper
SCCA national license tech
Millermatic 250X
1985 Toyata MR2 being prepared for STU
I am an SCCA tech inspector that has seen some VERY bad welds. First, in the SCCA General Competition Rules (GCR) the roll cage tubing size is determined by the car weight and class. In the case of Spec Miata the minimum size is 1.5 x .095 DOM tubing- NO ERW. These rules take bends into account. The bends must be a minimum of three times the diameter of the pipe. The number of attachment points is determined by the car class, in my case STU is limited to eight. The maximum area of attachment plate in all planes is 144 sq. in. and the maximum thickness this year is 1/4 in. (After several SM's put 1 in. plate in the right rear to get better corner weights.)
Wall thickness can now be measured with an ultrasonic thickness tester BUT, as was mentioned, it can be difficult to use properly. If the wall thickness is measured by drilling a hole make sure the bit does not strike the far wall as that will make the measurement too thin. Maximum hole size is 1/4 in., 3/16 in. preferred and anything smaller will not accept the depth rod of the caliper.
Second, all points mentioned about practice are good. In my case practice doesn't seem to help and I will have a professional welder do all the welds except for the attachment plates. I would definitely recommend building the cage but having a professional welder do all the tubing joints. If possible get a tech inspector to recommend a welder because not all road race car shops have good welders. If a car builder insists on welding his own cage I recommend going to a Community College welding program. He should also cut apart his practice joints to check for penetration, etc.
Gussets have not been mentioned but I highly recommend them. My car will have the maximum number of gussets per joint allowed which is two (SM is also two but other classes have no limits). Also any number of braces are allowed as long as they attach to only the attachment plates or the cage tubing and triangulation really helps.
Finally, what ever competition you are in be sure and get the rules, read them and ask questions before doing something that might have to be undone. If you ever think that you might change classes or sanctioning bodies try to prepare the car so that you don't have to tear every thing out and start over. We had a lawyer that thought he could do his own thing and found out that he couldn't change the rules to suit him.
John Cooper
SCCA national license tech
Millermatic 250X
1985 Toyata MR2 being prepared for STU
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