Learn me: roll bar for $2012 challenge

[Edit: My initial questions have been answered. Feel free to respond, though, if you have tips for DIY fabricating a bar (which scares me....I expect it takes much better welding skills than chassis fabrication) or recommendations for people/companies in central FL to make one.]

I may have to put a roll bar in my 1932 datsun replica.....not because it will be fast enough to need it (it definitely won't), but because I can't think of any other way to mount the seat belts. (I would not need belts/harness to be street legal in FL, but will need them to enter the $2012 challenge.) I've been looking at the roll cage/bar materials thread, so I expect that I will need to have it made of DOM.

What I need to know is:
- How high up the sides of the main hoop I should put the diagonals that slant to the back?
- What range of angles is permissible between the main hoop and those diagonals?
- can those diagonals be curved, or do they need to be straight?
- does the main hoop need a "harness bar" (I'm thinking about three point belts and not a harness)

See page 16+ of 41. It is NHRA legal requirements. I know you are not building toward that, but it should help (sorta) answer your questions of bars and fitment.

http://www.nhra.com/UserFiles/file/General_Regulations.pdf

What I need to know is:

• How high up the sides of the main hoop I should put the diagonals that slant to the back? Within 5 inches of the top of the rollbar

• What range of angles is permissible between the main hoop and those diagonals? At minimum 30 degrees

• can those diagonals be curved, or do they need to be straight? I've seen curved ones

• does the main hoop need a "harness bar" (I'm thinking about three point belts and not a harness) All cage structures 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 inches below, and not above, the driver’s shoulders, or to side bar

Gasoline wrote: See page 16+ of 41. It is NHRA legal requirements. I know you are not building toward that, but it should help (sorta) answer your questions of bars and fitment. http://www.nhra.com/UserFiles/file/General_Regulations.pdf

"side bar must be included on driver's side" ???? I'm sure that I've seen challenge cars that were not required to have a sidebar.

In reply to JoeyM:

Were they running fast enough to need to meet those rules?

JoeyM wrote:

Gasoline wrote: See page 16+ of 41. It is NHRA legal requirements. I know you are not building toward that, but it should help (sorta) answer your questions of bars and fitment. http://www.nhra.com/UserFiles/file/General_Regulations.pdf

"side bar must be included on driver's side" ???? I'm sure that I've seen challenge cars that were not required to have a sidebar.

I don't think Challenge cars have to be NHRA legal? I do think the NHRA rulebook is helpful as guidance to the general rollbar questions you had. Convertibles only need a rollbar 13.49 seconds and faster.

Got it. Sorry I misunderstood your intent.

JoeyM wrote: Got it. Sorry I misunderstood your intent.

No harm at all. You have a really cool build. I wish I could help. I can't wait to see it done. T

Ok, their rules say:

4:10 ROLL BAR All roll bars must be within 6 inches of the rear, or side, of the driver’s head, extend in height at least 3 inches above the driver’s helmet with driver in normal driving position or be within 1 inch of the roof/headliner in the area above the driver's helmet, and be at least as wide as the driver's shoulders or within 1 inch of the driver's door. Roll bar must be adequately supported or crossbraced to prevent forward or lateral collapse. Rear braces must be of the same diameter and wall thickness as the roll bar and intersect with the roll bar at a point not more than 5 inches from the top of the roll bar. Crossbar and rear braces must be welded to main hoop. Sidebar 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 inches below, and not above, the driver’s shoulders or to 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 .125-inch steel plates on top and bottom of floor bolted together with at least four 3/8-inch bolts and nuts, or weld main hoop to rocker sill area with .125-inch 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 driver’s helmet may contact it while in driving position. Adequate padding must have minimum 1/4-inch compression or meet SFI Spec 45.1. All cars running 180 mph or faster, SFI Spec 45.1 mandatory.

Based on that, I'd say the answers to my questions are probably:

• How high up the sides of the main hoop I should put the diagonals that slant to the back? (not more than 5 inches from the top of the roll bar.)
• What range of angles is permissible between the main hoop and those diagonals? (unspecified)
• can those diagonals be curved, or do they need to be straight? (unspecified)
• does the main hoop need a "harness bar" (yes)

Continue reading foward to section 20.25

Also you can call the local drag strip and ask for the name and number of one who "Certify's roll bars/cages". He should be happy to answer any fitment questions you have, even if you do not intend to race the car.

Thanks. Good plan.