Every aspect of automotive design has more depth and complexity than most people will ever realise. Whether it's exhaust systems (bore, length, bends), brakes (heat range, size, weight) or diffs (open, progressive locking, electronic), they all have a dramatic effect on the way that a vehicle performs and that's why it's so easy to screw things up with modifications that apply 'performance solutions' from one walk of motoring life (typically race or rally) to something completely different (ie: road cars). As PJB has well explained, there's much more to all of this than meets the eye.
I used to run a heavily track-focused Subaru (late 90's, when you had to import the hairy JDM spec cars personally) and it was an awesome car at the Ring, which was where we spent pretty much every spare weekend for nearly 10 years. It ran on some special road-legal tarmac rally tyres called Dunlop Formula-R D01J's and the grip they had when up to temp was truly outstanding. But they were based on a slick race carcass and ran lower than normal pressures - about 24/25psi I recall. When parked overnight the 'flat-spot' that formed during the cold and wet hours would take about 20 minutes to disappear when driving the next morning, so those first miles were accompanied by the vibrating percussion thump in quadraphonic surround sound..... All very Race & Rally but utterly ridiculous when I think about it now. Hey, but I was young then....
