NHRA-legal roll bar

This topic will cover a 5-point roll '''bar''' as opposed to a roll '''cage'''. Most fellows these days will go ahead and build a cage while they have the welder and their tools fired up, but we'll cover the bar for those of you who don't plan on going 9's (or quicker). With an otherwise '''unaltered''' floor and firewall, a 5-point bar will take you to 10.00 flat. If the floor is '''altered''' in excess of 4 square feet (not counting wheel tubs or stock removable floor panels which are bolted, in such as transmission removal panels on a pickup truck) or the firewall is altered in excess of 1 square foot, then a roll '''bar''' will take you to 11.00 and a roll '''cage''' is required at 10.99.  

All roll bars must be within 6" of the rear, or side, of the driver's head, extend in height at least 3" above the driver's helmet with driver in normal driving position and be at least as wide as the driver's shoulders or within 1" of the driver's door. Roll bar must be adequately supported or cross-braced to prevent forward or lateral collapse. Rear braces must be of the same diameter and wall thickness as the roll bar and intersect the roll bar at a point not more than 5" from the top of the roll bar. Crossbar and rear braces must be welded to main hoop. Side-bar must be included on driver's side and must pass the driver at a point midway between the shoulder and elbow. Swing-out sidebar permitted. All roll bars must have in their construction a cross bar for seat bracing and as the shoulder harness attachment point. Cross bar must be installed no more than 4" below, and not above, the driver's shoulders or to the side bar. All vehicles with OEM frame must have roll bar welded or bolted to frame; installation of frame connectors on unibody cars does not constitute a frame; therefore it is not necessary to have the roll bar attached to the frame. Unibody cars with stock floor and firewall (wheeltubs permitted) may attach roll bar with 6-inch x 6-inch x 0.125-inch (1/8") steel plates on top and bottom of floor bolted together with at least four 3/8-inch (0.375") diameter bolts and nuts, or weld main hoop to rocker sill area with 0.125-inch (1/8") reinforcing plates, with plates welded completely. All 4130 chromoly tube welding must be done by approved TIG heliarc process; mild steel welding must be done by approved MIG wire feed or approved TIG heliarc process. Welding must be free of slag and porosity. Any grinding of welds prohibited. See illustration. Roll bar must be padded anywhere drivers helmet may contact it while in driving position. Adequate padding must have minimum 1/4-inch compression or meet S.F.I. Spec 45.1. All cars running 180-mph or faster, S.F.I. Spec 45.1 mandatory.

Some fellows will build their roll bar only to protect the driver if their car is a purpose-built race car that will never have a passenger (unlike a car which will also be run on the street), so they build the bar to look sort of like a pyramid, except rounded on the top where it protects the driver's head. They will run the main hoop (B bar) up from the driver's side sill to the roof, make a half-circle around their helmet and then take the bar down to the sill at the other door instead of running it to the other side of the roof of the car and then down. This arrangement is just that much more work when you decide to go faster and make a cage out of it. The part of the rule that says "at least as wide as the driver's shoulders or within 1" of the drivers door" is meant for the "pyramid" guys. The part about being within 6 inches of the rear of the driver's head is to prevent a builder from installing the bar back at the rear window or up by the windshield with no other protective bars in between. You might have to picture the roof being caved in. If the bar is near the driver's head, he will be protected. By the way, let's get the terminology in order. The main hoop is normally referred to as the "B" bar, as that's where the B pillar is on the car. The windshield frame is the "A" pillar or A bar and the rear window frame is the "C" pillar.

Forward or rearward "lozenging" or collapse is prevented by the two diagonal (as viewed from the side of the car) bars (rear braces) which connect to the top of the B bar and run down through the package tray and into the trunk area in the rear, or into the floor of the bed if we're talking pickup truck, forming a triangular support to the B bar when the car/truck is viewed from the side. Lateral (sideways) collapse is prevented by the cross bar which runs from the left (or driver's side) of the B bar to the right (or passenger's side) of the B bar. This cross bar is installed at the driver's shoulder height with the driver seated in his/her driving position. It should be noted that many builders also install a diagonal bar (as viewed from the front or rear of the car) from the "B" bar corner at the driver's helmet down to the other side of the car at the bar end/floor to further prevent lateral failure.  

If you're not an expert welder, then hire a professional. It'll be the cheapest wages you'll ever pay for a nice roll bar installation. Nothing is cheezier than bird-crap welding. And don't even think about grinding any welds on the car. Hire a pro. If you fit up all the bars in the car and tack them in, the pro welder won't be there long doing a proper job. If you have fit the bars properly, there won't be much room at the roof to weld completely around the B bar/rear brace connections, so you may as well plan on gusseting these. Use 1/8" (the rule calls for 0.110" minimum) chromoly or mild steel flat plate of a triangular design with the long (unwelded) side of the triangle measuring at least 1 3/4". Use two gussets at each rear brace (four gussets in total) and you'll be bulletproof. By the way, NHRA now allows these rear braces to be bent (one bend only) to a maximum of 30 degrees '''(needs confirmation)'' so that the guys with street/strip cars can retain the back seat in the car for double dates and such. Most guys will run the rear brace bars from the B bar intersection back at a shallow angle to the roofline and then make a turn down and through holes in the package tray to the trunk floor, where the bars are terminated on 6 x 6 plates which are welded to the trunk floor. Now, you know what's going to happen don't you? Some guys from down off the farm are going to hear about this new lax interpretation of the rule from a buddy who didn't tell them about the "one-bend-only" part of the rule and they'll run the rear braces back from the B bar right up against the roof and make a 90 degree turn through the package tray and then another turn to terminate the bars on their plates somewhere on the trunk floor. Multiple bends in the bars will allow them to kink-up and will render them incapable of preventing the B bar from "lozenging" forward or backward. And the problem will be that there is little or no tech inspection at most drag strips, so they'll get away with it until they get to Firebird and get trailered. Then they'll raise a stink with the front office about how they passed tech at Podunk Dragway. You either have a race car or you have a street car -- '''make a decision!'''