GT4 class cars are mostly what can be referred to as track day cars, which are factory-built race cars available to the public. However, custom-built cars based on production models can also be built by teams. All cars are test driven by the FIA and then modified so that they all have near identical performance levels. Once a car has been approved by the FIA, it cannot be modified by the teams, eliminating continual development costs for constructors. All cars run on regulated Pirelli tires and Continental tires to further equalize performance.