A lowered car may put extra stress on various other suspension and steering system parts, leading to excessive wear and even premature failure. Tires may rub against sheet metal or suspension parts, causing damage to both. The ride will almost always be harsher, as most lowering methods reduce spring travel.

Since the factory shock absorbers aren’t valved to match the increased aftermarket spring’s rate, they won’t be able to dampen the motion of the spring properly. Additionally, installing a set of lowering springs on stock shock absorbers can also lead to premature wear.

Lowering your car a half inch to an inch and a half is not enough to ruin your fenders or hurt your stock suspension. Most manufacturers have built their lowering springs to work with stock suspension without having to upgrade every component to make up for the suspension drop.

Unlike lowering springs, coilovers offer a much greater range of adjustability including ride height, spring pre-load, shock damping, and rebound. Typically, coilover sets feature even stiffer spring rates than a set of lowering springs alone, again sacrificing ride quality for cornering performance.

Registered. It really does depend on a number of factors, like how low, how many miles on the shocks, road conditions, etc. OE Shocks with OE springs generally start losing damping around the 50k mile mark.

Under current NSW law a vehicle’s suspension can be raised or lowered by up to five centimetres without an engineer’s approval, and by up to 15cm with an engineering certificate.

Just lowering front would not really help handling. Lowering STi’s in general is detrimental to handling. As you stiffen things up you have to be careful as the rear inside wheel can lift if the rear is excessively stiffened, especially sway bar wise.