do cage support "boxes" count as mounting plate area?

T

tom91ita

New member
i have seen many cage pics lately with a "box" that supports the hoop, etc. this looks like a good way to get better access to weld the bottom of the hoop, front tube down by the A piller, etc.

not sure what part of the rules allows this. if it is the reinforcing plate then does the box count as part of the area? and for those that do this, is there anything "in the box" to prevent it from being "crush-able"?

correct section right?

9.4. ROLL CAGES FOR GT AND PRODUCTION BASED CARS
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3. Mounting Plates
a. Mounting plates welded to the structure of the car shall not be less than .080 inches thick nor more than 0.25 inches thick. The maximum area of each mounting plate in
the Improved Touring, Showroom Stock, Spec Miata, and Touring classes shall be 144 square inches. Plates may be on multiple planes but shall not be greater than 15 inches on any side.​
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It has been my understanding that all of the material used in "box" is subject to the area limits.
That being said, while it does make it easier to weld I don't believe it is as strong of mounting configuration as a flat plate, plates mounted at more than one plane. To me it is like welding knives edge down to the floor of the car. As opposed to a much larger flat surface that is supporting the load in a roll over scenario. YMMV
 
i am thinking about the following method (sizes approximate for discussion purposes);

roughly a 4" by 4" plate welded to the floor of the car.

make a 2.5" "cube/box" to support the main 1.5" OD hoop. this will be made by welding the four sides to the plate leaving the "top" of the box open until the next step.

the "top" will have a 2.5" long piece of tubing welded to it that will be inside the "box" when done.

now the 4" by 4" plate will have any roll-over impact spread across the both an area equal to what the tube would have had due to the "insert" plus the "box"
 
First, I have never seen any SCCA tech person measure the plates.
The square in rule, is the area covered by the plates, IMHO. not the plate area.
Most of the current vertical plates/boxes, are designed to tie into the sill plates and the floor. Keep in mind that the floor has almost no structural value on most modern cars.

The above box is a good idea, but way too small,of course. The improvement would be to build the multi sided plate, up the sill, insert the tube as described but leave a 1/2 gap to the box bottom. I consider any more than 1/2 in to be too much movement.
This now forms a "crush box", allowing the hoop to crush and move the impact loads to the rest of the cage before hitting the bottom of the box. The sole intent is to reduce the punch through potential , by spreading the loads to the other members.
 
I measure them. IMHO, if the box (normally called a plinth) is wholly contained within and welded onto a plate (or plates) that are welded to the chassis of the car, then I do not count the plinth area in the mounting plate square inches. If the plinth is welded to the mounting plate and/or some part of the chassis directly then I count the plinth area as part of the mounting plate square inches.
 
Our tech measure the area of the various plates that make the plinth. It isn't easy in all cases, but it can be done.

The rules clearly allow for creation of these structures:

"Plates may be on multiple planes but shall not be greater than 15 inches on any side."

And I think you'd be remiss in not using them. A box structure welded on three sides to strong portions of the chassis is far better than a single plate welded to the floor.
 
The contact area of the car's structure, should be the only measured area of the square in rule.
" shadow".
It was designed to keep the cage plates from stiffening the car.
What you do inside of the 144 in , is only regulated by the 15in max side rule.
If you have guys measuring and adding the sides of the hoop/ base plate/box, etc, contacting the car structure, than I really think the rule is misinterpreted.
 
If you trace the total area of the plates on paper and lay it out flat it must fit in the required area. Up 6', over 6' and down 6' is 18 per the rules. You can get creative with the bends to gain room.
 
tom91ita said:
i am thinking about the following method (sizes approximate for discussion purposes);

roughly a 4" by 4" plate welded to the floor of the car.

make a 2.5" "cube/box" to support the main 1.5" OD hoop. this will be made by welding the four sides to the plate leaving the "top" of the box open until the next step.

the "top" will have a 2.5" long piece of tubing welded to it that will be inside the "box" when done.

now the 4" by 4" plate will have any roll-over impact spread across the both an area equal to what the tube would have had due to the "insert" plus the "box"
Click to expand...

generally good thinking, but take full advantage of the plate area that you are allowed! You should see some of the plates in my car, even Kessler thought I was crazy!!
 
Check the web for good ideas on box design. There are a couple of forums out of Australia (VW racing I think) that have good concepts on proper design to avoid "kinfe" problems etc. IIRC they actually have a requirement that these are used.

As for the original question, I assumed it's the area of the plates that attach to the car. I think that would be hard to prove wrong. But I'm under the 144 sq in either way - that's a lot of room.
 
tom91ita said:
i am thinking about the following method (sizes approximate for discussion purposes);

roughly a 4" by 4" plate welded to the floor of the car.

make a 2.5" "cube/box" to support the main 1.5" OD hoop. this will be made by welding the four sides to the plate leaving the "top" of the box open until the next step.

the "top" will have a 2.5" long piece of tubing welded to it that will be inside the "box" when done.

now the 4" by 4" plate will have any roll-over impact spread across the both an area equal to what the tube would have had due to the "insert" plus the "box"
Click to expand...

Tom, what problem are you trying to solve? If its ability to weld the top tubes easier, there's two approaches that work well.
1. Use a hole saw, and cut holes in the floor. Drop the cage through, weld the top, then raise back up and weld in your floor plates
2. Do like we did in the lex, and bend the top tubes a touch to bring the tube end lower on the hoop.
 
thanks for all the comments.

i do plan on using most of the allowed area. the dimensions noted were for discussion. i will likely "count" any box support area as part of the allowed area since it will not be that much and better safe than cutting out part of it....

i like the idea of any "inner" tubing section being a 1/2" shorter for some allowable deflection/crushing.

Dave, one area of welding would be for the landing by the "A" pillar where i want to get very close to the rocker. if i "build" that up a bit with a "box" then that weld would be much easier. i really kind of liked what Greg (i think?..) had done with landing that support on the rocker panel as well.

if the reason we can build the "box" is because of the allowed area, i don't see how i cannot count it.

question just for grins, if i built it up to be 5" high under the main hoop, would anyone think that would pass tech? it could still meet the area requirements etc. but i do not think it would pass tech. bascially, at what point does a "box" stops being an attachment point and becomes part of the support structure?
 
Please do this. Call SCCA and talk to club tech. get names.
Verify that the sq in is the shadow cast on the car structure.( as I read it)
The "box" is not currently addressed in the rules . Many boxes are as tall as the sill top to floor size. . 5-8 in, is not uncommon.

I have a patent pending on the "crush box" for bolt in cages.
 
tom91ita said:
...bascially, at what point does a "box" stops being an attachment point and becomes part of the support structure?
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The moment it becomes a rollcage tube.

There are only two GCR-allowed basic elements in the rollcage design: the tubes and the mounting plates. If it's not a tube, it's a plate, and the plate is subject to area limits.

GA
 
Flyinglizard said:
The plates are( should be) measured by shadow, not the sq in of the multi sides.
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They are not. If they were, then they could be three feet tall.

The "boxes" are measured by total surface area, just as if they were plates mounted flush to the vehicle's structure. Any other way is contrary to the regulations.

GA
 
As Greg stated, see post 10. That is the way it has been explained when the new rule was crafted. The idea is to limit the area away from the attachment point that can be used to structurally reinforce the chassis. If the SQ inch rule was gone we could legally seam weld the entire car to the cage and run 1/8 wide plates down every seam of the car. Rule is well written and does what it is intended to do. Not so hard to do a very safe design within this allowance. If you went by a shadow I could run all the way up the down tubes so you can see how it goes crazy quick.
 
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