Roll bar help (stop me from being stupid)

In reply to Fladiver64 (Forum Supporter) :

Is that just for the main hoop? I don't see a way to do that without being rectangular on the diagonal forward to the rocker.

DeadSkunk (Warren) said:

OK. I've red and reread the cage section in that PDF and can't find the answer to my question.....how fast can a car with a 1.75" roll bar and a complete new floor /firewall go? I could put in a complete cage, but I'm short of material, so the roll bar option is preferred as long as the cage requirement doesn't come into effect at any ET I can hit.

The answer you seek is not in the General Regulations cage section(sec21, pg22), hence much confusion!

gumby said:

Section 4A pg.5 is pertinent to us

Fladiver64 (Forum Supporter) said:

In reply to Toyman01 (Forum Supporter) :

Mounting plates are 6x6 .125 min. I was told 36 square inches does not have to be a square.  I tried to get the plate on at least two surfaces, like the floor and then up the rocker for added strength.

I'm not sure that's an nhra requirement. Pretty standard for sports car stuff I think, but I don't remember seeing any spec on the size of the plates for nhra.

In reply to Robbie (Forum Supporter) :

This is from the NHRA rule book, says 6x6 plates top and bottom if bolted or just top if welded. I was told that the 6x6 is not as important as long as it is at least 36 square inches, but not all of the information I have been given has been true. I went larger just to be sure.

In reply to Fladiver64 (Forum Supporter) :

Right, it almost reads that size doesn't really matter if it's welded in.

In reply to Robbie (Forum Supporter) :

That's the way I read it, as well. 

I would make the plates 36 sq in at a min, if you need to make a rectangle not an issue. 

In reply to Fladiver64 (Forum Supporter) :

Mr Nelson agrees with you, so as far as I'm concerned, it must be gospel.

Fladiver64 (Forum Supporter) said:

In reply to Toyman01 (Forum Supporter) :

Mounting plates are 6x6 .125 min. I was told 36 square inches does not have to be a square.  I tried to get the plate on at least two surfaces, like the floor and then up the rocker for added strength.

Ok, so 5"X7.25" works, right?

I've got a 5" crossmember across my car, and the only other option I'd have is  a box hanging off it.

Does anyone know about the where the forward and rear diagonals attatch to the rocker, and (in my case), rear strut tower? Surely not 36 square inches as well.

For what it's worth, I asked Andrew Nelson, and he agreed with 6X6. Good enough for me.

In reply to wheelsmithy (Joe-with-an-L) :

I followed the same rule at least 6x6 everywhere a bar attached to the body.

Thread resuscitation inbound.

The way I read this diagram, The the maximum measurement from the top of the roll bar to the top of the down bar (brace, as they call it), as opposed to center, or bottom of the brace. Yeah, I'm splitting hairs, but this could make all the difference when fitting it.

Does the hive agree?

And to split another hair, what I read above is that 6X6" plates (top and bottom) are for when the bar is welded or bolted to just the floor. Roll bar can be welded directly to frame. So, where does that leave a unibody car? The correct answer is probably 6X6X1/8" plate as previously said by those in the know, and I don't mean to be argumentative, but am trying to get my mind firmly around this. 

To be continued...

Here's what I'm looking at on the forward diagonal braces. I've got 2" width of rocker, and to even get that, I'll have to build a partial box. I have a hard time believing the top panel of that box needs to be 2"X18" (for 36 sq.in.) total. Again, not trying to argue, simply trying to understand. 

My forward brace will connect with the rocker somewhere in the middle of the door opening, probably just a bit towards the front.

Here's what Robbie did on his X, only the diagonal brace goes up beyond the front of the door opening, and a plate about this size is more what I envisioned as the top of the box I would build. Maybe 2X6"

Thoughts?

yeah, the sill tops are narrow. You don't have to keep the whole 6x6 in the same plane. so make an 'L' shape plate, or even a 'Z' to go up the side and down the sill a bit.

Mine's, er, probably not the best example to follow. haha.

oh, and on the top of the diagonals below the top of the hoop, I read it the same way, top to top. But yeah, it's not exactly clear.

The rules are intended to give a solid base , the 1/8" thickness, and a good amount of weld length to hold it to sheet metal. Robbie is correct in that the plate area doesn't need to be in one plane. I'd cap the sill and run plate vertically down the inner sill to the floor. You end up with a solid mount that the tube won't punch through and two feet of weld length holding the whole structure to the sheet metal, spreading the load.

Thanks for the answers, guys. I guess I was only counting the top plane of the box, but if in two planes, with an area of 36 sq in, I think I've got it.

I think I was going to argue that the roll bar rules only call for one forward diagonal, and since I was doing two, I could cut the plate area in half. 

Probably was a dumb argument, but I was struggling to remember why I made that plate the way I did. 

In reply to Robbie (Forum Supporter) :

Didn't mean to put you on the spot. Yours is a thread I know I can find some X1/9 shots that show my conundrum.

We're all learning here.