Rules state:

"Each mounting plate shall be no greater than one hundred (100) square
inches and no greater than twelve (12) inches or less than two (2)
inches on a side. Welded mounting plates shall be at least 0.080-inch
thick, and must contain an inspection hole of 3/16” diameter. Plates
may extend onto vertical sections of the structure. Any mounting plate
may be multi-angled, but shall not exceed one hundred (100) square
inches total including vertical sections. Each mounting plate must have
an area of not less than nine (9) square inches. Each mounting plate
must be welded around its entire edge."

As I understand there is a sub discussion on this with "Help Need It" thread, but I was wondering what everyone else thought regarding boxed in plates versus flat plates? Why do most of the cages run with flat plates versus boxed in plates?

The why is a plinth mount allows you to weld the top nodes all the way around and then jack the main hoop into place and then weld the plinth in underneath it. Makes for tight to the roof main hoop. Also gives greater chassis rigidity by tieing the main hoop into three planes instead of two. Plenty of pics in the other thread.

The flat plates seem to have been a "that is the way we always did it" design choice from lower end cage builders. A lot of times really good fabricators/welders have been asked to do cages even though they have no knowledge of good cage design. You end up with a cage that is pretty, has very good welds, and looks functional to the layman, but has no engineering/analysis behind it's design and in the event of an incident may be more harmful than helpful.

If you find a guy that says he can build you a cage on the cheap be wary. If he can bend tubing and weld very well take him a design that is engineered and get a quote on building that specific design. Then do not let them take shortcuts or move bars around. Great designs are turned into junk if we move this tube a couple inches this way because I can't get my welder in there and move this one a little because my notcher won't do a node that tight. You can pull a really good design off of these pages and then get a local welder to follow the design and end up with a nice safe cage.

Rules state:

"Each mounting plate shall be no greater than one hundred (100) square
inches and no greater than twelve (12) inches or less than two (2)
inches on a side. Welded mounting plates shall be at least 0.080-inch
thick, and must contain an inspection hole of 3/16” diameter. Plates
may extend onto vertical sections of the structure. Any mounting plate
may be multi-angled, but shall not exceed one hundred (100) square
inches total including vertical sections. Each mounting plate must have
an area of not less than nine (9) square inches. Each mounting plate
must be welded around its entire edge."

As I understand there is a sub discussion on this with "Help Need It" thread, but I was wondering what everyone else thought regarding boxed in plates versus flat plates? Why do most of the cages run with flat plates versus boxed in plates?

Perhaps it's because the rules of most series specifically say that the plates must be mounted to the floor. From the above...how can something extend onto a vertical section if it is not on the floor already?

I should say "perhaps it's in part......"

The flat plates seem to have been a "that is the way we always did it" design choice from lower end cage builders.

That's not necessarily accurate.

I agree with Bryan. I don't consider a NASCAR shop that builds tube cars from the ground up "low end cage builders".

James Posig
JMT TrackCars
#231 GTS 2

Jack,

So then boxed up plates are illegal? Or does it depend on various tech inspectors? Spec Miata guys do it, which come from SCCA rules, BMW rules are almost a carbon copy of SCCA rules regarding the cage details.

The flat plate on the floor method can work to get a cage tight to the roof line if you cut holes in the floor to drop the whole cage down. This allows access to 360* of the joints for welding. The cage is then raised up and the floor plates slipped under to hold the parts together.

There's also no reason why both methods can't use 3 planes at the main hoop. A-pillar only has 2 planes available though - regardless of plate or plinth.

Regardless of the method, the rockers will need to be cleaned, sealed, painted.

Jack,

So then boxed up plates are illegal? Or does it depend on various tech inspectors? Spec Miata guys do it, which come from SCCA rules, BMW rules are almost a carbon copy of SCCA rules regarding the cage details.

I suppose it probably matters how it's done. I saw one car this past year where the boxed in sections were not touching the floor.....IE they were flat at the top where the tube came in, it extended down a ways, then it angled over to meet the corner where the floor/side meet. Essentially the tube was mounted to the side.

Most cars I saw this past year have the typical floor mounted plate which then extends up the side. So the tube runs close to the side such that it's welded to the plate all around then up the side as well.

I'm not sure that boxed plates are noncompliant as a general rule but certainly the execution matters!

Edit: To me, this is something I'd ask about before doing it. It's not a cheap or easy thing to undo.

I think in most cases it comes down to construction technique. You have to be able to weld the top of the bars close to the roof and there are only a few ways to do this. These are making the cage fit in such a way to have suffecient acces to the top of the cage to make a weld, cutting the floor where the bars go and droping the cage threw them and then welding the tops and you cover the whole in the floor with a plate, cutting the roof open above the area needed to be welded or the whole roof off and finally using the boxed plates. In most cars you can achive the same multiplane strength using flat plates bent or added too similarly to the base of the boxed plates as you can with well done boxed bases. It seems it all comes down to builders prefrences and the construction of the car.

There are some other techniques.

Here is how the E90 WTCC's are done, this obviously can't be done with a main roolhoop, however the idea of taking a section, tacking it in, finished all the tubes, then removing it, fully welding it, and welding it back into place is a viable alternative.

http://www.terato.com/cars/info/bmw320si/dev/P0025391.jpg

"I suppose it probably matters how it's done. I saw one car this past year where the boxed in sections were not touching the floor.....IE they were flat at the top where the tube came in, it extended down a ways, then it angled over to meet the corner where the floor/side meet. Essentially the tube was mounted to the side."

Jack,

Did this car pass tech inspection?

"That's not necessarily accurate."

Bryan,

Care to go into details why it is not accurate?

Andrew,

Thanks for your imput again... your cage is a bolt in but if you were to go with a weld in version, would you prefer boxed plates over flat?

"I suppose it probably matters how it's done. I saw one car this past year where the boxed in sections were not touching the floor.....IE they were flat at the top where the tube came in, it extended down a ways, then it angled over to meet the corner where the floor/side meet. Essentially the tube was mounted to the side."

Jack,

Did this car pass tech inspection?

You don't honestly think I would answer a question like this in any public forum let alone this one do you? ; ) I guess I should not have gotten involved in this discussion. It just didn't occur to me that this could be much of an issue. I don't recall how many cars I looked at this year but I only recall seeing the one that I mentioned above with construction like this.

Sorry, I won't participate in this thread any longer.

You don't honestly think I would answer a question like this in any public forum let alone this one do you? I guess I should not have gotten involved in this discussion. It just didn't occur to me that this could be much of an issue. I don't recall how many cars I looked at this year but I only recall seeing the one that I mentioned above with construction like this.

Sorry, I won't participate in this thread any longer.

LOL. I laughed a bit when I read the question, but you don't need to be uncivil, Jack. ;)

LOL. I laughed a bit when I read the question, but you don't need to be uncivil, Jack. ;)


Oops, sorry, I forgot the smiley, wasn't trying to be rude! ; ) (an extra one just in case)

"That's not necessarily accurate."

Bryan,

Care to go into details why it is not accurate?

Because there are plenty of excellent cages that don't use boxed end plates, including BMW Motorsport, Porsche Motorsport, and the cage in our car. Specter makes it sound as if the lack of boxed end plates means the cage was designed by a lower end cage builder.

Does Porsche, BMW, etc Motorsport cages don't use boxed plates due to the chassis floor strength? I know a lot of Spec Miata cages run a boxed plate.

Jack,

I've sent you an e-mail. Hope to hear a reply back. :)