Forza Horizon car classes and PI explained (D to X)

PI is a single number from 100 to 999 that rates a car's overall performance. The higher the number, the more capable the car is judged to be. A 999 is the fastest, most extreme end of the scale; a low-100s car is a slow, stock everyday vehicle.

That one number is a blend of several traits: top speed, acceleration, braking, handling and launch (how well the car gets off the line). The game weighs all of these together to land on a final figure. This is why PI is only a rough guide and not the whole story — two cars can share the same PI while getting there completely differently. One might be a straight-line rocket with clumsy cornering, the other a nimble handler that runs out of top speed. Both can read, say, 800.

Keep that in mind when you pick a car from a code: PI tells you the ballpark, but the balance of speed versus grip is what decides whether a car suits your driving style and the track in front of you.

Forza Horizon groups every car into a letter class based on its PI. The bands are fixed and have stayed consistent across the series, so once you learn them they carry over:

D class: 100 to 500. C class: 501 to 600. B class: 601 to 700. A class: 701 to 800. S1 class: 801 to 900. S2 class: 901 to 998. X class: 999.

D is the entry level — stock road cars and slow classics. As you climb through C, B and A you move into progressively quicker machinery, with A class covering a lot of the sweet-spot sports cars. S1 and S2 are the high-performance and hypercar territory, and X is reserved for the single highest rating of 999, the wildest builds in the game.

Notice that the top classes are narrower than the bottom one. D class spans 400 points because there is a huge range of slow-to-moderate cars, while X is a single value. That is worth remembering: the higher you go, the less headroom each class gives you.

A car's PI is not fixed. Fitting upgrades — a bigger turbo, lighter panels, better brakes, stickier tyres — raises the traits PI measures, and so it raises the number. Add enough and the car crosses a class boundary: an A-class car at 780 can become an S1 car once a few upgrades push it past 800.

This is the core of building for a target. You rarely leave a car fully stock or max everything blindly. Instead you choose upgrades that lift performance while keeping the PI where you want it — usually just under a class ceiling.

Downgrades work the same way in reverse. If a build overshoots its target class, tuners will remove or soften parts to bring the number back down, trading a little raw power to stay legal for a given event.

Most races and online lobbies are restricted to a single class so that cars compete on roughly even terms. An A-class-only race means everyone brings a car rated 701 to 800; nobody can show up in a hypercar and walk away with it. The class cap is what keeps the field fair and the racing close.

This is exactly why a car sitting just under a class ceiling is so prized. A build at 800 PI is at the very top of A class — it is the strongest car allowed in an A race. A build at 801 is technically faster, but it has been bumped up into S1, where it is now one of the weakest cars in a much quicker field. That single point can be the difference between dominating your class and being outgunned in the next one up.

Good tuners obsess over this. They squeeze as much performance as possible into a build while landing right on the ceiling — 500, 600, 700, 800, 900 — to get maximum capability without tipping over into the harder class above.

Every tune you download with a share code was built to a target. The creator picked a class and PI on purpose — an A-class 800 drift setup, an S1 900 circuit build, a B-class 700 cruiser — and tuned the car to hit it. When you browse tunes here, the class is one of the first things worth checking.

The practical rule is simple: match your build to the tune's class. A tune designed for an 800-PI A-class car assumes the car is at that performance level. If your copy of the car is still stock, or upgraded differently so it lands at a different PI, the tune's gearing, suspension and balance were calculated for a car that no longer matches — and it will not behave as intended.

So when you grab a code, note the class and PI it was built for, apply the matching upgrades to reach that figure, then load the tune. That is how you get the result the creator actually made, and it is why we label the class on every tune we list.