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Appendix A – Roll Bar Specifications
Divisional Requirements: A Roll Bar is mandatory in the Auto A Division and recommended for vehicles in the B division. Vehicles with “pop-up” roll bars, approved OEM rollover structures, or factory reinforced roll structures may be allowed to compete without a roll bar in classes where a roll bar is required but will be evaluated on a per car basis. The Race Director’s decision is final.
Basic Design Considerations: The basic purpose of the roll bar is to protect the driver in case the vehicle rolls over. It should be designed to prevent serious body shell deformation in the case of a collision or of the car turning over. A roll bar is comprised of a structural frame or hoop and mounting points.
The top of the roll bar 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 not be less than fifteen (15) inches apart, inside dimension, at their attachment points to the uppermost main chassis member.
If certification of roll cage construction cannot be provided, an inspection hole of at least 3/16 inch diameter must be drilled in a non-critical area of the roll bar member to facilitate verification of wall thickness. This should be at least three inches from any weld or bend.
Material: The roll bar 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, 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. It is not sufficient to simply attach the roll bar to a single tube or junction of tubes. The roll bar must be designed in such a way as to be an extension of the frame. Considerable care must be used to add as necessary to the frame structure itself in such a way as to properly distribute the loads. It is not true that a roll bar can only be as strong as any single tube of the frame. On vehicles of frameless construction, consideration should be given to using a vertical roll bar hoop of 360 degrees completely around the inside of the car, and attached with suitable mounting plates. This type of roll bar then becomes a substitute for the frame.
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Bracing: The braces must be of the same size tubing as used for the roll bar itself. All roll bars must be braced in a fore or aft direction with the brace attached within six inches of the top of the hoop, and at an angle of at least thirty (30) degrees from vertical. It is required that a diagonal brace be used to triangulate the main hoop and it is highly recommended that this brace be attached at the top on the driver’s side, and to the bottom on the “passenger’s” side.
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