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Appendix B – Roll Cage Specifications
Roll Cage Division Requirements: A Roll Cage is mandatory in the Auto Unlimited division.
Design Requirements: Roll cages must be designed and made so that, when correctly installed, they substantially reduce body shell deformation and so reduce the risk of injury to occupants. The essential features of Roll cages are sound construction (designed to fit the particular vehicle), adequate mountings, and a close fit to the body shell. Tubes must not carry fluids. The safety cage must not unduly impede the entry or exit of the Driver.
Bolt-in roll cages are allowed; fully welded cages are recommended. At least one door bar must be used on both sides of the vehicle. The use of a NASCAR style door bar incorporating at least 2 bars that extend into the door and are supported by vertical upright bars is recommended. A factory side impact bar may only be removed if using a NASCAR style cage design.
The cage should be triangulated at as many points as possible and the liberal use of gussets, welded at each joint, is mandatory.
Basic Design Considerations: A roll cage is comprised of a structural frame or hoop, a perimeter roof hoop, door bars, fore and aft bracing and diagonal supports all arranged in such a manner so as to prevent occupant injury in the event of a rollover and to structurally improve the integrity of the vehicle.
The top of the roll cage main hoop shall not be below the top of the driver's helmet in a closed car and a minimum of two (2) inches above the driver's helmet in an open car when the driver is in the normal driving position with helmet on. It shall not be more than six (6) inches behind the driver.
The two vertical members forming the sides of the hoop shall attach to the outermost main chassis member. If certification of roll cage construction cannot be provided, an inspection hole of at least 3/16” diameter must be drilled in a non-critical area of the main hoop to facilitate verification of wall thickness. This should be at least three inches from any weld or bend.
Material: The roll cage hoop and all braces must be of seamless, ERW (Electric Resistance Welded), DOM (Drawn over Mandrel) or CREW (Cold Rolled Electric Welded) mild steel tubing. Chrome alloy tubing, such as 4130, can be used but is not recommended since the strength of the area adjacent to the welds will be impaired if the structure isn't normalized, and because of the difficulty in making satisfactory welds. The size of the tubing to be used must be determined on the basis of the weight and speed potential of the car. Refer to chart below. The main hoop and support braces must be of the same size.
Fabrication: The main vertical hoop must be of one continuous length of tubing with smooth continuous bends and no evidence of crimping or wall failure. All welding must be of the highest possible quality with full penetration and will be subjected to very critical inspection. Arc welding, preferably TIG, should be used wherever possible. Gussets should be welded at the junction of any tubes.
On vehicles of Space frame or Frameless Design: It is important that the structures be attached to the vehicles in such a way as to spread the loads over a wide area using spreader plates. It is not sufficient to simply weld the bars to body or frame material. The roll cage must be designed in such a way as to triangulate the designed structure of the vehicle. Considerable care must be used to add as necessary to the frame structure itself in such a way as to properly distribute the loads.
Bracing: The braces must be of the same size tubing as used for the roll bar itself. All roll cages must be braced in a fore or aft direction with the braces attached within six inches of the top of the verticals and at an angle of at least thirty (30) degrees from vertical. It is required that a diagonal brace be used to
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