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Vehicle Safety Equipment
Roll Bar Specifications
Roll Bar: A Roll Bar is mandatory in the Grand Sport Division and recommended for vehicles in Touring and Grand Touring. All open top vehicles in all classes are required to have roll bars. Vehicles with “pop-up” roll bars, approved OEM rollover structures or factory reinforced roll structures may be allowed to compete in the Grand Sport Division without a roll bar 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, particularly heli-arc, 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.
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.
An additional horizontal bar to support the main hoop is recommended. In addition, this bar should be installed at the height no more than 2” above or below the driver’s shoulders while seated in the driver’s position. The shoulder harness should be attached to this bar.
Mounting Plates: Roll bars and braces must be attached to the frame of the car whenever possible. Mounting plates must be used for this purpose. In the case of cars with unitized or frameless construction, mounting plates must be used to secure the roll bar structure to the floor of the car. The important consideration is that the load be distributed over as large an area as possible, with 4”x 4x1/8” the minimum size desired for spreader plates. A back up plate of equal size and thickness must be used on the opposite side of the panel with the plates through-bolted together using grade eight (8) bolts and Self-locking nuts or double nuts if welding is not possible. It is preferred that the plates be tack welded or welded to the car's frame. On some vehicles this exact size is not an option and square area of the spreader plate must be calculated to spread the maximum load expected in the worst-case scenario.
Removable Roll Bars: Removable roll bars and their braces must be very carefully designed and constructed to be at least as strong as a permanent installation. The removable sections MUST “bottom out” onto the mounting plate so as not to put all of the stress on the connecting bolt.
If one tube fits inside another to facilitate removal, the removable portion must bottom on the permanent mounting, and the mounting hardware used to secure each joint must be at least grade eight (8) or better. It is recommended that the telescope section be at least eight inches in length.
Other Designs: Deviations from the above will be considered.
Roll Bar Padding: Roll bar padding must be used to protect the occupants in all areas of possible contact. It must be of material (readily available) that is designed for this purpose. SFI-approved padding is highly recommended.
Minimum Tubing Sizes: The size of the tubing to be used shall be determined on the basis of the weight and speed potential of the car. NHRA-size tubing of 1 5/8” by .132 wall mild steel may substitute for the mild steel sizes listed in the chart.
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