View Full Version : street/track roll bar safety

09-27-2006, 04:36 PM
I have read as much as I could find on roll bars and cages and have decided to go with a 4 point roll bar in order to mount harnesses on my 68 firebird. I ran it for the longest time with no roll bar and a y type harness to the back seat area and am tired of the risk.

I am wondering how all of you have yours set up and about the problems with passing tech. I have a 2" main hoop and a 1 3/4" main hoop with either 1 3/4 or 1 1/2" bars for the rest of it. I will weld the main hoop to 6x6x1/8" plates that will be welded to the floor and wil triangulate to the subframe connectors. where should the back down bars weld to and how big should those plates be? Is it worth it to run side bars for added side protection but more body to bar risk?

The car will be a weekend car with the occasional track day for now but I might race it more seriously later when money allows.

09-28-2006, 02:52 PM
Maybe I should rephrase this a little. I am interested in hearing more of a continuation on the "Achy Breaky Heart" sticky above.

I doubt Im alone in wondering more about specifics in safety for a car that will see more than the light commute. All of our vehicles on this site need more safety than what was offered originally, and most of our vehicles need more safety than what is currently offered in modern cars because our cars are capable of a lot more than the typical street commuter.

This brings me to the dilema that has been hashed repeatedly. If we need more safety, where do we turn. The next step up from 3 point belts is a 5 or 6 point harness. The safest way to mount one is to a roll bar. A roll bar/cage adds risk of body to bar contact in the case of an accident. So where is the compromise.

I am thinking of compromising like many of us here have with a four point roll bar with additional supports to the subframe connectors, and maybe removeable side impact bars.

My question comes down to specifics. It seems to me from what I have read that a 1 3/4 diameter main hoop is a big enough diameter for most racing sanctions but some might require that as a minimum, so 2" might be required in some cases because bending crushes the bar a little. I have also read that scca(i think) requires all the tubing to be the same, so if you have a 2" main hoop the rest would have to be 2". Wall thickness is probably ok at 0.120" What to choose for tubing?

The next question is about placement. NHRA requires the main hoop to be within 6" of the back of the drivers helmet, but on the street this puts the drivers head within 8" of less without a helmet from the main hoop. Is the solution to meet the 6" requirement with the seat waaay back and move it forward for the street? Or do you say screw the requirements I care about my head, and move the main hoop farther back? Or are the modern sfi roll bar foams enough to provide safety while keeping to tech regulations?

So to summarize,
1) Which tubing or assortment of tubing will be most likely to pass tech inspections whithout compromising safety on the street?
2) Where is the best place to put the main hoop to please your head and inspectors?
3)Anymore helpful insight to add to the roll bar/cage discussion?
4)Anyone know of crash testing done with racecars?

Steve Chryssos
09-29-2006, 12:08 PM
The SCCA has requirements and recommendations. When reading their guidelines, be sure to pay attention to their language (i.e. "must" vs. "suggests")
Mandatory: The SCCA requires 1-3/4" x .095" wall DOM seamless tubing for all vehicles over 1500 lbs and .080" thick mounting plates if welded. They also require that the main hoop be braced to prevent for aft movement. Read the language, and you will see that they are looking for a four point. The language looks for the bracing to go towards the back of the car. (You should anchor the braces to the framerails.) They say nothing about requirements for a second set of braces heading forward. Six inches behind driver's head is mandatory. Use high back buckets to protect your head.
Suggested: The rulebook suggests a "Petty Bar" which is a diagonal in the main hoop that limits side to side bending. You will also need a horizontal bar to properly mount belts.

As for actual technical inspection at track days, I only have drag race and auto-x experience. I have always found the tech inspection process to be lax at these "non-competitive" events. So if your main hoop is 7" back instead of 6" back, I doubt you will get busted.

09-29-2006, 12:42 PM
I agree with streetfytr68. I have never be questioned on a roll bar at any track before. The only place I can see some one wanting more bar is if you run 9,s or quicker in the quarter. As far as road courses go, I run driving schools. (clubs) and they do not require a bar unless it is a convertible. Randy

09-29-2006, 08:59 PM
Just the people I was hoping to hear from. Thanks for your help.

As for the rear down bars, I am going to weld them to plates that are welded near the axle centerline on the "framerails" if we can call them that in a f body. I have not heard a requirement for the size of these plates.

I noticed how jeep wranglers come with roll bars that are not that far from the drivers head and started wondering about that today. I have just started to scratch the surface on the results of their crash testing but so far I have not seen any offset, side or rear impact results, only frontal impact. That might shed some light on the issue of roll bar safety without helmets.

The ultimate plan is to use structural foam in the a pillars and other hollow structural spaces to acheive strength like a cage without the metal bars everywhere, but still the 4 point bar for harnesses is necessary.

I have become really interested in safety because it seems so little is actually known about it in our hobby. Dedicated race cars have perfect guidelines to follow but there are none that I can see for the guy that will drive mostly on the street but needs more safety for those high speed runs on the track. I hope more people will share their experience here.

09-30-2006, 07:14 PM
How is that 56 coming along????
I still want to buy that when its finshed or somewhat close!

Speed Raycer
10-07-2006, 06:53 PM
Hotrodder... first and foremost is that you need to pick a main ruleset to follow to keep the tech guys happy. If you go with 1.75x.095 for the SCCA, the NHRA tech guy might toss you when you hit the dragstrip as they require .118 min. wall. If you go with the 1.25 harness bar that the NHRA allows, SCCA might say "no way" as they require (depending on which class you run) the same size tubing as the main hoop on all required bar. It can get confusing.

Also, the 6x6x1/8" pad is an NHRA thing. In SCCA rules they give you a max. square inch for the plate and you can get nice and creative with the plate and tie into multiple planes and structural points. If you're building the car for track days you want to think of load paths and use the rollbar to your advantage and try and hit the points that your suspension is acting on---- but always keep the safety of the drivers/passengers in mind.

Any other questions, feel free to ask!

10-07-2006, 09:53 PM
^^wow...you build some cool stuff. I like the cages on your website! Thanks for the response

Jim Nilsen
10-08-2006, 04:27 AM
One point to remember is that the 2in. bar will only weigh about 5lbs. more and the other tubes will be much easier to weld to it without the roof getting in the way as much. It might not seem like much but it really would have been easier for me to weld the other tubes and it keeps it all legal no matter where you go for tech and if you ever decide to go with more tubes and heavier stuff the main hoop can remain.

Jim Nilsen

12-16-2006, 08:40 PM
Jim, just noticed you are from Rockford,Il where at neighbor, maybe we can get together and share our projects. Dan

12-17-2006, 06:31 PM
How do racing bodies view cars with t-tops or sunroofs? are they in the same class as convertables?