After tyres, your brakes are some of the most important areas of a car to look at when it comes to modifications. Even high-spec performance cars can be slightly under spec'd in this area once you start driving on track or putting more power into the car due to the increasing amount of heat generated by the brakes. With the right combination of parts, you will still have a set of brakes you can trust long after the original set-up has faded.
With a set of performance brakes from EBC Brakes or Brembo, for instance, you can also enjoy much better initial pedal feel. Your factory brake pads will probably have been designed to be economical for normal driving and won't necessarily perform all that well once hot. A set of aftermarket or performance brake pads will typically offer increased bite and higher maximum operating temperatures, both important for performance driving.
A performance brake disc from Black Diamond with a surface designed to keep the surface of the pad clean and allow hot gases to escape is a great complement to an uprated pad. Braided brake lines from a manufacturer like Goodridge will make sure no braking force is lost to bulging or worn brake lines. As brake fluid ages, it absorbs water, so replacing your existing brake fluid with a suitable replacement or an uprated fluid with a higher boiling point are also advised.
Of course, the ultimate upgrade is a complete big brake kit which is a full overhaul of your car's brakes. An AP Racing big brake kit features all of the above, plus much bigger calipers and allows everything to be scaled up, proving to make a real difference in terms of heat dissipation and stopping power.