Lighter = Faster (N/A build thread #2)

[WE3RX7]

Originally Posted by infernosg

The shop has some interesting ideas about the roll bar. I need to look into the NASA and SCCA rulebooks to see if it's legal, but maybe someone here knows. I want to keep the bar bolt-in but I wanted more strength at the attachment points so I asked the shop to weld some 3/16" or 1/4" plates to the car. They came up with a neat idea to build little boxes at the attachment points with welded nuts inside. This way the attachment points should be much stronger and I won't have bolts going through the body of the car. Legal?

So, the question of legal or not relies on what you intend to do. You mentioned NASA events, but what kind of events? I hopefully don't offend, but if you are not TT licensed yet or higher, your car isn't even required to have the roll bar. You can run through the HPDE groups and even run around in HPDE 4 when you get there and the roll bar is just added safety for yourself. The question here shouldn't be if it is legal or not, but if you feel like that design would be safe. Generally, bolt in bars for convertibles (or coupes) need to have at least an 1/8" foot mounted to a plate no thinner then .120" covering 18sq/inches attached (welded) to the body. Now for some, that .120" surface IS the floorpan, etc. I don't personally trust it, but hey.. that's what is considered 'legal' and it does work ok for rollover protection.

That being said, if your body shop fabs a box (very common in weld in cages) that is 1/8" thick, the mounting foot on the roll bar is 1/8" thick and the hardware being used is all Metric 10.9 or SAE grade 5 or 8... I'd say you would pass any visual tech inspection. The entire idea is so that the bolt in cage/bar doesn't punch through the floor of the car in a roll over.

On another topic... if you're serious about track use, weld it in. You can even just weld in the bolt in cage/bar w/ the proper footing/reinforcements. We used an autopower 4pt bolt in roll bar in a NASA ESRC rally B-stock FC a long time ago. When we started competing, we just welded in the cage and added the appropriate additional points of attachment per ESRC rules.

The bolt in roll bars are good for mounting a harness to, and if properly installed, can be ok during a rollover, but they are not something I would trust for side impacts (going off, hitting a tree, concrete wall, another car, etc). Those bolts will just snap off.. what's worse still, say you go off.. have a hard lateral impact and THEN flip over... not good my friend. This just happened to a ford at Summit Point last year.. his bolt in cage snapped at the attachment when he went off before the bridge and hit a tree and proceeded to roll around (he lived, FWIW)...

I'm not trying to be a downer, I've used bolt in cages/bars and am even considering adding one to my RX8 now but I think it's important you really consider what you want to do with the car. If its getting added protection, chassis stiffening, harness mounts, etc then a properly installed bolt in is ok. If its serious motorsports (PT/TT), weld that guy in there and put it out of your mind.

Hope this helps... nice build so far man... I've always liked your updates!

[infernosg]

Originally Posted by C. Ludwig

The SCCA rule book is available for free download and the cage rules are pretty well defined. NASA basically copies SCCA safety rules. I think, kind of like ASSuming, you need backing plates on the underside of the floorpan for bolt-in cages. The lay-engineer in me likes your idea but I don't know if it will pass tech.

Jealous of a clean FC shell. Makes me want to build another ITS car.

Yep, read through both the NASA CCR and SCCA GCR and came to the same conclusion. The mechanical engineer in me agrees with you but you can't argue with the rules. While the regulations are for "competition" and I don't plan on going any higher than TT I'd rather conform to the competition rules than do my own thing and get constantly questioned about it.

The shell is pretty clean - definitely better than I though it would be considering it spent it's life in WI! Next time I'm at the shop I'll snap some pics of the trouble spots.

Originally Posted by WE3RX7

(snip)

See above. I was progressing through HPDE when the red car blew up back in '11. I don't plan on building this to be competitive in any particular class but I'll likely do a TT every now and then to compete with friends. This will be a "weekend fun car" only. Otherwise, I understand where you're coming from completely.

The roll bar I have (Kirk Racing), when used as intended, conforms to all SCCA and NASA regulations. I understand it won't ever be as strong as a welded-in cage but I'll still have some semblance of an interior and want the convenience of being able to remove the bar as needed. Since I plan on taking this to the occasional meet (e.g. DGRR) I don't want to have to climb over/around bars ever time I get into/out of the car.

I asked the shop to weld 1/8" plates to the floor pan and rockers to strengthen the mounting points and they came up with the idea I described above (basically a plinth box for a bolt-in cage). A quick Google search didn't find anything similar but the CCR and GCR were both pretty clear about the need for backing plates.