NHRA-legal roll bar

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 through the cab rear window/rear cab sheetmetal onto 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 and also serves as the shoulder belt anchor point. It should be noted that many builders also install a diagonal "D" 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 structural 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. Any grinding on the cage material or the welding joints will turn the entire thing into junk. 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!'''