The carbon fiber bottom plate is designed to accept CRC's new AR pivot system (33741, 33742, 14091) . This new Adjustable Roll-center pivot system allows you to shim the rear pivot up and down by adding shims and washers. Shims included to raise the front and rear pivot to 2mm.  Up (more shims) for more cut and steering, down (less shims) for more rear grip and a more locked in feel. This #1866 bottom plate fits and converts the 1502 and 1802.