Disc grooves and sometimes cross drilling are frequently used on racing brake discs to clean the surface of the pad and allow gases produced to escape.
In doing so the friction characteristics are modified, different groove and &drilling patterns affect the friction characteristics in different ways, some affect overall friction and others the bite or release characteristics and therefore the best solution is not necessarily the same for each application.

AP Racing is constantly developing and refining disc face patterns. The most popular face types are shown below:-

P = Plain, (No grooves or holes) Mainly used on road applications where low noise is vital	G4, 8 12 & 24 = Grooved, (Straight forward facing) Digit specifies number of grooves per face. Traditional style grooves.
CG4, 8, 12 & 24 = Curved grooves, (backward facing) Digit specifies number of grooves per face. New standard pattern.	CR4, 8, 12 & 24 = Curved grooves, (backward facing, running out on outside diameter to clear debris. Only used on thick wall discs). Digit specifies number of grooves per face.
D = Cross drilled, drilled holes chamfered). Still preferred with some pad materials but can compromise disc life.	GD = Grooved and drilled. Usually used on road applications.
RD = Radiused drilled, (cross drilled but with a radiused run out to reduce noise and improve life compared with standard drilling patterns). Mainly used for aesthetic reasons on road applications.	RA = J hook design. Gives improved bite and debris clearance and reduces distortion / vibration, outer grooves run out to outside diameter. Thick wall discs only
GA = J hook design. Latest design gives improved bite and debris clearance and reduces distortion / vibration, outer grooves do not run out to outside diameter.	RC = 'J' hook design. As RA design but with 3 hooks across face. this design gives improved bite and debris clearance plus reduces distortion / vibration. thick wall discs only. Outer grooves run out to outside diameter.
GC = 'J' hook design. As RC design but with 3 hooks across face. this design gives improved bite and debris clearance plus reduces distortion / vibration. thick wall discs only. Outer grooves do not run out to outside diameter.

N.B. Not all face types are available for every disc.