Could anyone tell me a bit about the difference in 1 piston and 2 piston rotors please? Looking at converting my stock system to a full APR racing kit. Thanx guys/girls

Well, simply put 1 piston clamps at 1 spot, 2 would clamp in 2 spots.

the pistons are in the callipers not the rotors. multi piston callipers provide more even pressure spread across the brake pad causing better pad/disc contact.

sorry guys, woke up this morning relising i wrote the wrong thing, mean't to say what's the difference between 1 piece and 2 piece rotors? Sorry to stuff you around

2 piece rotors usually have an alloy centre hub bolted to a ring style rotor.

The 2 peice would have fully floating disks, which all modern motobikes use at the front. The disc is held in place with rivets to a hub that connets to your axel. Benefits would be less heatsoak in the caliper through the mountings, also the ability to use different metals for different purposes, such as a matched metal to the pad material for optimum fiction, instead of having just a solid lump of cast iron. Racing brake maintence costs might be cheaper as well, as you just change the disc and not the whole assembly, not to mention servicing time might be lower too. Only very expensive and elaborate braking systems have such setups on cars, so you have to consider if your car is a true circuit/track car or a street/show pony ? If doing some club stuff, then you might be able to get away with a well matched street application. You wouldnt need such brakes on the street, well matched pads and slotted rotors are good enough. If you lock your brakes up all the time, you have effectively lost any benefit in the race brakes, as the main friction slowing you down is between the pad and disc, and the wheel to the road. Road tyres are fairly limited in grip and the roads are not smooth at all. Less weight with optimisation in materials is also a benefit in racing.