Roll Cage Rule Question. SCCA, NASA, EMRA
 

I am building my first custom cage in a '90 GXL and attempting to build the cage to meet road racing rules for SCCA Improved Touring, NASA Performance Touring, and EMRA. I'm 75% complete with my cage build and other than some weld access issues that need to be resolved I have one big concern. SCCA's 2012 rules now state "Roll cage may not pass through any structural member..." This of course is open to interpretation but I'm concerned with my front down tube mounting points but it's not too late.

In order to maximize clearance between driver and cage the cage had to be made as large as possible. To gain weld access to the top of the cage a hole was cut through the rocker and floor below the front down tubes so that the cage could be tipped down through the floor of the car (pictured below). The plan was to plate the floor to cover the hole and weld the cage tube to the mounting plate. Then I would box in the rocker around the tube and weld the tube again to the top plate of the box where it was passing into the rebuilt rocker. Structurally this seems like the strongest thing to do for the cage but I want my car to pass tech. Anyone know if this approach is allowed?

Reference the second picture posted by 'cagedruss' of "Road Race Josh's Second Gen" here:
https://www.rx7club.com/race-car-tec...395960/page11/
I planned on the tube being welded at the top of the box and at the bottom plate that I would set the box on. Alternatively, I could cut the tube shorter and only weld it at the top of the box if this is the only way to pass tech.

Thanks for your help!

I have heard of this technique and it should be strong as hell. I see no issues with SCCA tech on this method.

Depending on how you rebuild that area you can make it look like your tube is sitting on top of a box built to fit the rocker.

Don't ask, don't tell.

Thank you very much for your input.

For more clarification this can be found in the roll cage attachment point section (9.4.E.1) of the SCCA GCR. This statement about passing through a structural member was added in 2012. The one exception they make is ...except miata rear main hoop braces may pass through the package tray.

The way I see it is that what I'm doing is technically welding the cage into the rocker, without passing through, after everything is welded back up of course.

The build is progressing as quickly as it can for a weekend warrior. I'll post some pics to the roll cage pic thread and link them here in the next week or so...

If there is anyone out there that has a different interpretation of this rule and thinks I'm about to break it, speak up! it's not too late for me to cut the ends off those tubes and weld them to the top only. The proposed method just seem much safer for a tube that's asked to do a lot in a roll over.

My understanding is that the rule was made so that someone couldn't just pass the down tube through the rocker and run a bead around it. There was a Mini driver killed at a vintage event in Florida when it went roof first into a barrier and the tubes just punched through because of no plating or gussets. The idea is to spread the load over as wide an area as possible. You shoud be fine with a plate under the tube and tied into a box on the rocker. I would add a couple of gussets just for insurance.

Yeah cutting that area was a mistake, you cut out the main structure of the car to get to the flimsy floor area.

Build a big 4 sided box to fit into the area you cut out (slightly larger in all directions) and weld it on all sides to the chassis. It will look like you welded a box over the stock unibody rails, as mentioned, which is prefered.

Land the tube on the top of the box with enough room for a 360 deg weld. The biggest rule we DQ cages for in nasa is the 360deg weld rule. So if you put the box over the tube passing it all the way to the floor it would be hard to weld 360 without cutting out structure at the point where the door mounts, also you would have to notch the top of the "box" to put it over the tube.

Also put in your 7 and 8 pt bars at a 45 and land them on 6x6 plates on the area of the pan at the front of the footwells that is at a 45 deg angle, the main structure of the unibody crosses this point to the front frame horns. This adds huge ankle and foot protection in a crash as well as rigidity.

Chad Martin
Chief of Tech (Chief Scrutineer), NASA Midwest

Thank you Chad for the clarification. I would like to provide further explanation of my original plan and I would very much appreciate your additional insight.

I agree that cutting into the rocker was by no means ideal but by properly plating and re-welding that area, the structure will be returned. This method was a compromise that allowed me to gain 360 degree weld access to all the top cage joints while maximizing clearance between cage and helmet as well as the cage and my legs. I am very safety conscious with this cage build which is why I didn’t just go buy a bolt in kit and bolt it to the floor (legal) or a weld in kit that welds to the floor (also legal). I also agree that I have definitely made my job more difficult than if I had brought those tubes inboard and built plinth boxes to set them on afterwards but that would have put these tubes closer to my legs, so much so that my ankle would have been rubbing the plinth box or downtube when depressing the clutch pedal. In a bigger car this would not be an issue.

The original plan was to weld a plate to the floor, both around the perimeter of the hole from underneath the car and on the top side around the perimeter of the plate with the plate being much larger than the hole of course. The down tube would then be 360 degree welded to the top of this plate. A vertical side plate would be welded to the side of the rocker overlapping the sheet metal on each side of the opening I created and also sit on top of the plate welded to the floor and fillet welded to this plate. Two additional plates would be cut to fit around the perimeter of the downtube and overlap the sheetmetal on either side of the opening in the top of the rocker and be welded to the following; both plates welded together(where they meet at each side of the tube) to form a single welded top plate, the perimeter of this plate to the top of the rocker and the vertical side plate, and 360 degrees around the downtube. This will return the structure to the rocker and tie the downtube to the top and bottom of this box. All plates mentioned to be out of 12 gage steel.

Question #1)
Do I proceed as planned or do I do everything I said above except make the plate on the top of the rocker one piece (no welded seam in the middle) with no thru-hole and cut the downtube so that it welds only to the top of this box instead of the top and the bottom?

Regarding the forward braces. My original plan was to weld the forward brace to the downtube opposite the joint for the top door bar and run this tube forward, nearly horizontal and weld it to a formed plate in the top corner of the firewall that would tie the cage to the forward subframe, firewall, and cross car structure just below the windshield. The tube would be placed on this plate to be directly in line with the point where the forward subframe meets the firewall. I like your idea as well and wish I could do both but for some reason, probably limiting chassis stiffening affect, NASA PT and SCCA IT (my target classes) do not allow these additional points. Safety should be ‘king’ but I digress, I’m not here to argue the rule, only to be sure I do the safest thing possible within the limits of the rules.

Question #2) Is the downward diagonal forward brace welded to a plate over the junction of the rocker, firewall, and forward subframe safer than the higher horizontal tube I described above?

Thank you very much for your help!

Jeff

This is what i would do because it gives an inspector a readily visual, full 360 deg weld to a solid plate. Or at least that is what it will look like, which is what matters. What you describe in full really is a good plan but definitely make that plate on top with a hole in it that the tube passes through a single piece or you will be facing questions you don't want to be answering. Again, while i think in some respects your end result will be better, the inspectors are not suposed to make engineering judgment calls (even though i am an engineer) we are charged only with ensuring that a car meets the requirements in the CCR so that we can get insurance and all continue racing. If i let a car out on track that is not constructed per the requirements of the CCR then we open ourselves up to liability as an organization.

This is exactly the way the cage is constructed in my FC, with those forward braces intentionally landed to the beefy part of the unibody where it crosses from the side rocker heavy frame areas to the horns extending to the front of the car. Basically the frame narrows up at this point as we all know. Anything higher on the chassis in my opinion is not strictly a frame hard point on the unibody. It's all structure designed only to maintain the shape of the cabin, firewall, windshield, fenderwells etc..not true main car structure.

I'll take a picture of this area of my car tonight and post it here for your comparison.

-Chad

I have no problem doing this except that it will be difficult at this point (top of the cage is already welded) to make a plate with a hole that the tube can pass through that is still large enough to overlap the opening... it would have to be slid up the tube from the bottom so it wil probably have to be smaller than the opening. I could have a smaller solid plate (continuous around the tube) that welds on top of the large split plate that spans the opening in the rocker but this too may raise quesitons. If I can't figure out a creative way to make this happen I will have to cut the tube so that it sits on top of the plinth box with a solid top plate.


A picture of this would be much appreciated! Thank you for the additional insight and advice.

I think you could make that plate just small enough and slide it up the tube then build the rest of the box underneath it...should work...hard to say without being there in person. ;)

I think I will be able to do it. I have just enough room to shift the cage enough to fish that plate up through the opening, first one side then the other. I'll know this weekend when I plan to fab these plates.
I would really like to see a pic of your forward braces. I plan to finalize that this weekend too.

Thanks again.

Great news... I was able to fit a solid, one-piece plate on top of the rocker to properly mount the cage and rebuild the rocker and still overlap the material on both sides of the hole. It took some creativity and a lot of time but it's all fitted and ready for welding.

Sorry for the delay. Here are pics of the footwell area of my car for your reference.

Okay great! Thank you. I guessed really close. My tube will attach about 3-4 inches higher than that on the plate I have pictured here with the red circle being where the tube will land. After looking at your pics I can probably make the plate a little smaller, maybe take an inch off the top edge.