roll cage questions

I am building a cage for some friends and I am unsure about a few details.

The car is being set up for 2 seats for learning/training purposes so my question is should I double up the  diagonal bracing to suit...or are the single diagonals sufficient?  Obviously its not being competed with a passenger, but the risk is always there so I do not know.  I do not see anything in the rules about it.

Thanks for any help.

Edit....i should of been more clear.  The rear diagonal and the one within the main hoop.

The car is being set up for Gridlife Sundae cup (25:1) & SCCA.  I am trying not to weight it down more then necessary.  I am adding anti-intrusion bars up front regardless.

If there's nothing in the rules about it then it depends, the double brace will greatly increase the stiffness of the cage and improve crash safety on the sides, downsides would be slightly increased weight and massively increased entry/exit difficulty. If it's a newer car (with better safety and a stiffer frame) just doing track days you may want to go with the single diagonal to make it easier to get in and out of.

You may also want to think about where the rules are going. The double-diagonal frame may end up being more futureproof against the rules.

In reply to malibuguy :

Just to clarify, you're talking about the diagonal brace in the same plane as the main hoop?

IMHO, the single should be sufficient.  Just be sure you leave room on the harness bar for harnesses on both sides.  An 'X' brace rather than single diagonal may actually make that easier depending on the space you have to work with.

Ah I assumed this was about door bars. For a main hoop brace a single diagonal is fine and there's not much difference when adding a 2nd one.

I would look at the cages in rally cars as those are intended for two occupants.

My Datsun has a rally spec cage; it weighs 24lbs more than the equivalent road race cage would (there is 12ft of extra tube)

I usually put a diagonal within the plain of the rear supports that is opposite the one in the main hoop.

If you look at most roll over damaged cars, the top of the windshield always has way more damage than the center of the roof.

I edited the main post for more clarity.  Sorry I was rushing when I originally typed it 

I don't know if I'm more confused after your edit,lol.

Are you talking about putting an "X" in the driver's hoop or one diagonal in the hoop and one in the rear supports?

I haven't read the GCR closely recently but SCCA used to spec a diagonal in the hoop OR in the rear supports.

In reply to jgrewe :

Its all good, I suck at being clear sometimes lol

So the main hoop that is behind the driver...SCCA says at minimum one diag from passenger side up to the diode behind the drivers head.

For the rear down bars, it just states there should be 2 going down to essentially the rear strut mounts.  I figured on doing a single diag again to the diode behind the drivers head.

I am probably overthinking this.  Ive only done basic drag style cages before.

If you want to have some fun, you can read the FIA specs for cages. Lots of diagrams :) They do require two diagonals in the rear legs for rally.

Appendix J 2016 - Article 253.8 - Safety Cages (Groups N, A and RGT) - WMSC 04.03.2016

In reply to Keith Tanner :

I quite like this.  Thanks for the link

How do the sanctioning bodys feel about interlocking tube clamps like these?

https://www.summitracing.com/parts/tgi-180114-kit

Specifically, they'd be on the rear diagonal braces. 

There's a few designs out there. Any better ones?

Be careful using those. The shrinking/stretching/movement of the tubing during welding makes them shift more than you can imagine. I did a drag cage for a guy with an S197 Mustang and he wanted a removeable diagonal door bar. He bought 2 of those that I used. There was a bunch of filing to get it to fit after the weld joints cooled which really surprised me to be totally honest. Just beware if you do use them, but of course, this was just my experience so yours may vary.

In reply to lotusseven7 (Forum Supporter) :

As a fellow 7esque guy, you probably recognize the problem. I want a solid, lockable boot, which the diagonals also penetrate. There are a variety of ways to deal with it, but I thought that removable struts might be a good option.

Keith Tanner said:

If you want to have some fun, you can read the FIA specs for cages. Lots of diagrams :) They do require two diagonals in the rear legs for rally.

Appendix J 2016 - Article 253.8 - Safety Cages (Groups N, A and RGT) - WMSC 04.03.2016

Our e46 cages were built by someone who primarily does rally cages, and he showed us all the places our seemingly "complete" road course cages were short bars to be FIA rally compliant, or otherwise just not "rally" ready. 

He was a big fan of symmetrical braces anyone where he added them, if there was going to be a 2nd occupant. In main hoop, in roof, etc.