NHRA-legal roll bar

5 OR 6 POINT ROLLBAR CONSTRUCTION (NHRA LEGAL) (Required beginning at 11.49 with a closed car/truck, 13.49 with a convertible)

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. If the floor or firewall are ALTERED as described, then it only makes sense to get yourself an NHRA Rulebook and install a CAGE because you will only pick up 1/2 second with a BAR. (11.49 to 11.00). A "point" refers to a connection point of the end of a bar at the car floor or frame. A 5-point roll bar will have connections as follows: The main hoop, or B-bar, will connect to the sill/floor/frame/frame crossmember at two points just behind the driver, the two rear braces will make two more connections somewhere in the trunk area and the fifth point will be in the area of the driver's left foot, made by the driver's "side bar". Most of the time, racers will go ahead and install a sixth point "side bar" on the passenger side of the car, helping to stiffen the car up. One note of interest here, minimum O.D. of the tubing for a roll BAR is 1 3/4", for a roll CAGE it's 1 5/8", so it may be cheaper to buy all 1 5/8" tubing and build the cage from the start. Anyway, I'll start off with the rule for the bar:

2008 NHRA Rulebook, General Regulations 4:10 ROLL BARS: 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.

A. "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." 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 makes no sense to me. It's 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.

B."Roll bar must be adequately supported or cross-braced to prevent forward or lateral collapse." 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.

C. " 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." "Same diameter" means minimum 1 3/4" (1.750") "Same wall thickness means 0.118" for mild steel and 0.083" for chromoly "Not more than 5"....means do not move the rear braces over to the side of the car to the vertical part of the B bar any further down than 5" as measured from the top of the B bar. The closer to the top of the B bar these rear braces are, the better they can prevent the B bar from forward or rearward collapse (lozenging).