FH6 Tuning Glossary

Every Forza Horizon 6 tuning term, defined in plain English.

A quick reference for the language of Forza Horizon 6 tuning, from PI and ride frequency to aero balance and the current meta. If a term in one of our tuning guides is unfamiliar, it is defined here.

Performance Index (PI): A single number from 100 to 999 that rates a car's overall performance in Forza Horizon 6. PI decides which class a car races in.
Class: A performance bracket set by PI. FH6 classes are D (up to 499), C (500 to 599), B (600 to 699), A (700 to 799), S1 (800 to 899), S2 (900 to 998) and R (999).
Differential: The component that decides how the driven wheels share torque. Tuned with acceleration and deceleration lock to control traction and rotation.
Acceleration lock: How tightly the driven wheels are tied together on the throttle. Higher lock puts power down cleanly; in FH6 road racing it runs high, 75 to 95 percent for RWD.
Deceleration lock: How tightly the driven wheels are tied on lift-off. High decel lock causes corner-entry understeer, so road builds keep it low, 10 to 20 percent.
Ride frequency: How quickly the car bounces on its springs, measured in Hz. Setting springs from ride frequency keeps light and heavy cars consistent. FH6 tarmac runs 2.6 to 3.2 Hz.
Spring rate: The stiffness of a spring in lb/in or kgf/mm. Calculated from the weight over each axle and the target ride frequency.
Anti-roll bar (ARB): A bar that resists body roll on an axle. The front-rear ARB split is the fastest way to shift balance between understeer and oversteer.
Mechanical balance: A readout in the FH6 tuning menu summarising front-rear balance. Aim for 0.55 to 0.65, with 0.60 as the target.
Camber: The tilt of a wheel viewed from the front. Negative camber keeps the tyre flat through body roll for more cornering grip.
Caster: The backward tilt of the steering axis. More caster adds high-speed stability and self-centring, but too much dulls turn-in.
Toe: Whether the wheels point inward (toe-in) or outward (toe-out). Front toe-out sharpens turn-in; too much rear toe-in causes understeer.
Final drive: A master gear ratio that shifts all gears together. Raise it for acceleration, lower it for top speed.
Aero balance: The front-rear split of downforce, shown as a readout. The FH6 meta target is 0.40 to 0.45, roughly 40 percent front and 60 percent rear.
Downforce: Aerodynamic force pressing the car into the road for more grip at speed, at the cost of straight-line drag.
Understeer: When the front tyres lose grip first and the car pushes wide. Cured by softening the front, adding front grip and lowering the diff deceleration lock.
Oversteer: When the rear tyres lose grip first and the tail steps out. Cured by softening the rear or adding rear toe-in.
Rebound damping: How fast a spring is allowed to extend. Higher rebound controls weight transfer; usually set higher than bump.
Bump damping: How fast a spring is allowed to compress. Usually around 60 percent of rebound so the tyre absorbs hits without kicking.
Ride height: How high the car sits. Minimum on tarmac to lower the centre of gravity; raised off-road to clear obstacles.
Weight distribution: The front-rear split of a car's mass, which drives the spring and balance calculations. A nose-heavy car needs stiffer front springs.
Tyre compound: The type of rubber fitted, such as slick, semi-slick, sport, rally, off-road or drift. Off-road and rally are a road racing value meta at A class and below.
Centrifugal supercharger: A forced-induction upgrade that is currently the biggest performance-per-PI power item in FH6, almost certainly a bug, so it is the strongest power buy until patched.
Rivals: Forza's time-trial leaderboards, the yardstick competitive tuners build against.
Meta: The current best-performing cars, parts and settings, as proven on the leaderboards. It shifts with each balance patch and new car.