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.
Any vehicle's performance index can be increased by applying power-improving and weight-saving upgrades. Players can also decrease their P.I. value by adding weight and using a drivetrain conversion.
In the Forza Horizon games, there are no cars ranked X 999 by default.
Classes
| Class | FM2 | FM3 | FM4 | FH | FM5 | FH2+FF7 | FM6+FM6:A | FH3 |
|---|---|---|---|---|---|---|---|---|
| F | - | 100-200 | 100-200 | - | - | - | - | - |
| E | - | 201-275 | 201-275 | 100-200 | - | - | 100-300 | - |
| D | 0-400 | 276-350 | 276-350 | 201-300 | 100-400 | 100-500 | 301-400 | 100-500 |
| C | 401-550 | 351-425 | 351-425 | 301-400 | 401-500 | 501-600 | 401-500 | 501-600 |
| B | 551-700 | 426-500 | 426-500 | 401-500 | 501-600 | 601-700 | 501-600 | 601-700 |
| A | 701-850 | 501-600 | 501-600 | 501-600 | 601-700 | 701-800 | 601-700 | 701-800 |
| S | 851-998 | 601-700 | 601-700 | 601-700 | 701-800 | - | 701-800 | - |
| S1 | - | - | - | - | - | 801-900 | - | 801-900 |
| S2 | - | - | - | - | - | 901-998 | - | 901-998 |
| R3 | - | 701-800 | 701-800 | 701-800 | - | - | - | - |
| R2 | - | 801-900 | 801-875 | 801-900 | - | - | - | - |
| R1 | - | 901-999 | 876-998 | 901-999 | - | - | - | - |
| R | - | - | - | - | 801-900 | - | 801-900 | - |
| P | - | - | - | - | 901-998 | - | 901-998 | - |
| U | 999 | - | - | - | - | - | - | - |
| X | - | 1000 | 999 | - | 999 | 999 | 999 | 999 |