A. Main hoops shall incorporate a diagonal brace. The brace shall either be in the plane of the main hoop or extend from the top of one rear brace to the bottom of the opposite rear brace. Automobiles with mid-mounted engines can have the lower mounting point attach to the frame of the automobile within 6 inches of the main hoop. In the case of braces in the plane of the main hoop, the brace must span at least 50% of the width of the main hoop, and at least 75% of the height of the main hoop. In convertible vehicles with a production line beginning 1990 or later, such as the Mazda Miata, a “V” design, also known as a “double diagonal” used between the rear supports is acceptable.

B. Cars must incorporate a main hoop horizontal brace at the approximate level of the driver’s shoulders but not lower than the shoulder belt mounting point as described. If a double-diagonal “X” brace is used in the plane of the main hoop, a half-width horizontal brace may be used behind the driver’s seat to mount the seat back and shoulder harness.

C. Cars must have two (2) braces extending to the rear from the main hoop and attaching to the frame or chassis. Braces must be attached as near as possible to the top of the main hoop (not more than 6 inches below the top), and at an included angle of at least 30 degrees.

D. Open cars must have two (2) braces extending forward from the main hoop and attaching to the front hoop, not more than 6 inches below the top of the front and main hoop. It is recommended that the front and rear braces attach to the main hoop as close as possible to each other.

E. On cars where the rear window/bulkhead prohibits the installation of rear braces (e.g., Honda del Sol), the main hoop shall be attached to the body by plates welded to the cage and bolted to the stock shoulder harness mounting points. This installation design must incorporate a diagonal bar connecting the top of the main hoop to the lower front passenger side mounting point (Petty bar). Alternatively, the rear window may be removed and a clear, LEXAN™ replacement installed. The rear cage braces may pass through this replacement window and through the engine cover or bodywork to allow connection to the frame or unibody.