Australia is strict with car modifications. The only way around these is with a Engineers Certificate. He checks to see the cars modifications you've done are up to scratch.... This is usually quite costly and you pay whether he passes the car or fails it....
Things like:
You can only go 2 inches wider in rim size over factory...
Car exhausts must not be louder than 90dB..
Cant be lower than 100mm off the ground..
The first 3 I can think of that come too mind. If you get caught with these by cops with no engineers certificate you get fined. You then have to get the car back too a passable level of whichever rule you dont comply with, within a few weeks or its unroadworthy and you cant drive it.... :roll:
The joys of modified cars these days...