The Performance Index (commonly abbreviated as P.I. or PI) is a car performance measuring system first introduced in Forza Motorsport 2. It displays a vehicle's overall performance value, which is determined by top speed, acceleration, braking, handling, and launch rating, as well as weight. It is shown by letters (F to A, then S, R, P, U, or X) and then a number starting from 100 and capping at either 999 or 1000. In the Forza Horizon games, there are no cars ranked X 999 by default.