Forza Horizon 6 PI & Car Classes Explained: Why Tyres Jump a Class
What the Performance Index (PI) number means in Forza Horizon 6, the D–X car classes and their PI cutoffs, and why a tyre compound swap can jump your car several classes — plus how to build to a class cap.
The Performance Index trips up almost everyone at first. You fit one part, the number jumps, and suddenly your C-class runabout is barred from the C-class event you built it for. The part that feels broken — a tyre swap launching a car up two or three classes — is actually the system working exactly as designed. Once you understand what PI is counting, it stops being a surprise.
What PI actually measures
PI is a single number that rolls every performance trait of a car — top speed, handling, acceleration, braking, launch and off-road ability — into one figure, commonly running from around 100 up to 999. Your car’s class is just a band of that number. The game isn’t judging your driving; it’s totting up what the car is theoretically capable of and dropping it into a bracket.
That’s why two completely different cars can sit in the same class: a heavy, powerful cruiser and a light, nimble corner-carver can both land at, say, A 750 by getting there different ways.
The class bands (early, hedged numbers)
| Class | PI range (approx.) |
|---|---|
| D | up to ~500 |
| C | ~501–600 |
| B | ~601–700 |
| A | ~701–800 |
| S1 | ~801–900 |
| S2 | ~901–998 |
| X | 999 |
Because the game is new, treat the exact cutoffs as early and community-reported — they may be confirmed or nudged later. The ordering of the bands, however, has been consistent across Horizon titles, so the structure is safe to plan around.
Why every upgrade adds PI — tyres most of all
Each part you fit contributes to the index. Tyre compound is one of the heaviest single contributors, because grip touches almost everything the game scores: cornering, acceleration off the line, braking distance and launch all improve when the rubber sticks. So a jump from street to sport to race tyres doesn’t just nudge the number — it can add a large slice in one click.
On a low-PI car that effect is amplified. The same chunk of PI is a much bigger percentage of a 450-point D-class car than of an 850-point S1 car, so the lower the car starts, the more dramatic the class jump looks. A stock C-class car landing in A or S1 off a single compound change isn’t a bug; it’s the index pricing the grip you just bought. Different compounds carry different trade-offs — the drag tyres breakdown covers one case where the PI cost and the real-world benefit don’t line up.
How to build to a class cap
Most events are class-restricted, so the goal is usually to land just under a ceiling — A 800, not A 801. A maxed-out A-class car will beat a barely-S1 car in an A-class lobby every time.
- Open the upgrade screen and watch the live PI readout as you add parts.
- Fit the grip and handling parts you actually need first (see the tuning guide for upgrade order).
- Stop adding the moment the number approaches your cap.
Dropping back under a cap
Overshot? You don’t have to start over. Step the tyre compound back one level, drop a power or aspiration part, or swap a part for a cheaper version until the number falls under the line. Detuning down to a cap is normal and reversible — nothing about it risks your save or your car.
Quick tips
- Use the live PI readout religiously; it updates before you commit.
- Tyre compound is your biggest single lever, up or down.
- Build to the top of a class, not the bottom of the next one.
- If a build feels overspent, strip a part rather than rebuilding.
Pick a chassis that suits the class you’re targeting from the tier lists or the full car database, then tune it to the cap.
Frequently asked questions
Why does changing tyres jump my car up several classes in Forza Horizon 6?
Because tyre compound is one of the largest single contributors to the Performance Index. Grip feeds into cornering, acceleration, braking and launch all at once, so swapping to a stickier compound (sport, race, rally) adds a big chunk of PI in one move. On a low-PI car that one change can be enough to cross one or even two class boundaries.
What are the PI cutoffs for each car class?
The bands are commonly reported as D up to ~500, C ~501–600, B ~601–700, A ~701–800, S1 ~801–900, S2 ~901–998, and X at 999. Treat these as early, community-reported numbers for this new entry — the exact thresholds may be confirmed or adjusted, but the order of the bands is stable across Horizon games.
How do I build a car to an exact class cap like A 800?
Add upgrades while watching the live PI readout on the upgrade screen, and stop just below the ceiling. If you overshoot into the next class, remove or downgrade a part — often the tyre compound or a power part — until the number drops back under the cap.