Oversteer & Understeer
You can use downforce to increase grip levels at higher speeds, at speeds where you don't want to be surprised by sudden oversteer.
Downforce can be produced by adjusting the aerodynamics (windflow) of the car. The biggest gain in downforce can be realized by a rear spoiler, but at the cost of valuable aerodynamics. This can hurt the the top speed quite a bit, but it will deliver a much smoother, steadier ride at higher speeds.
Modifying other parts such as the hood, side fenders, underbody diffusers and other body panels usually improves the overall balance. The faster you go, the more important aerodynamics become.
VARIOUS BODY MODIFICATIONS TO INCREASE DOWNFORCE
If you lose the downforce, youll lose the grip. Ever seen a NASCAR race? When a car gets hit it loses its grip and as a result of that, it loses all of its downforce. Its not recoverable! Uncontrollably he crashes into the barrier.
Ever seen a F1 car lose its rear wing? Hardly any grip whatsoever! In both NASCAR and F1 they are heavily relying on downforce to increase their grip at higher speeds.
Heavily tuned street cars and high-end exotics such as Porsches and Ferraris resemble racing cars and also benefit from spoilers & aerodynamic modifications. Unfortunately function over form is often disregarded when people purchase new exterior parts.