AP Racing offer the following advice as a guide only for mounting and installing a Carbon/Carbon Disc.
The preferred mounting method for carbon discs is “ float in the bell” as this allows for axial and radial float between disc and bell. Radial float allows differential expansion of disc and bell thus reducing stresses in the disc.
The idea of axial float is to compensate for a certain amount of stub axle / upright flex by allowing the disc to take up its ideal position within the range of float thus avoiding ‘Knockback’ of the caliper pistons. However the float should not be excessive as disc gyroscopic loads can cause the same effect that the float is meant to alleviate. The amount of axial float will depend somewhat on the application. In a ‘perfect’ system with minimal disc movement relative to the Caliper the amount of float need only be around 0.45mm nominal float. The drawings opposite provide information on disc and bell mounting, typical mounting bell data and an example of disc and caliper ducting.