Disc Mods
Improving the performance of the disc itself has seen three types of modification - venting, slotting and drilling.
Vented discs have become pretty much a standard item on modern cars as a more efficient disc temperature wise can be fitted into a smaller area. This contradicts the 'bigger is better' principle, but modern technology has seen improvements in pad materials, so small cars that are fairly heavy can have good brakes without going to huge wheels to fit them in. The Metro for instance. A smaller vented disc does have slight advantages over a bigger solid disc in the effects of inertia stakes.
Slotting discs has been pretty much misunderstood by many. It is generally believed that the slots are there to improve cooling. They are not. They are there to wipe the pad surface. In operation, the heat creates debris and gases between the disc and pad surfaces - reducing their effectiveness. The slots clear this away. To be totally effective though they need regular cleaning as the debris fills the slots up. Now, it has become fashionable to have loads and loads of slots in discs. AP Racing recommend only four slots in a disc as small as the Mini. Bear in mind that friction area is needed to make the brakes effective - lots of slots markedly reduce the surface area of the disc and thus the available friction area...
Drilling discs is open to the same misunderstanding that slotting is. The same actual reasons apply, except that holes are more effective over time as they are more or less self-cleaning. The only major draw back (apart from going mental on the number of holes - friction area reduction again) is that in discs with insufficient mass - too small in diameter or too thin - they tend to crack and fall apart. I know motorbikes don’t have these problems, but they are a totally different kettle of fish! The 8.4” disc can be drilled - but needs to be done by experts, not at home in the shed - it's your life (and possible other's) that you're fooling around with.
