Forza Horizon 6 needs to rework the way PI is calculated and how PI classes are divided. These haven’t really changed since Horizon 2, as that game removed E class (still present in Motorsport games) and made all higher classes have a much higher PI. While there is some balancing factor to this, it is mostly caused by how the PI is calculated in the first place - I often feel like D500 cars in Horizon 5 perform similar to E275 cars in Forza Motorsport 4, that’s a numerical difference of almost half the PI range!
Forza Motorsport 3 and 4 should work as the benchmark for how PI classes ought to be divided in a Forza game. While it is understandable that many oddball cars, such as the BMW Isetta or the Peel P50, would be stuck at those games’ lowest rating of F100 with maxed out stock engines, I don’t see it as a negative. In fact, this would make “more powerful” slow cars more competitive against each other with less upgrades. Let’s also not forget that kei cars are set to appear in Horizon 6 - with the 64hp limit imposed by the government, they would fit perfectly next to Motorsport 4’s city cars in F class. The higher classes need extensive work too, as the performance difference between low S1 and high S1 PI cars tends to be higher than that between low C and high C PI class cars. Better PI calculation would tie in neatly with this new PI grouping, to provide a more accurate description of the cars’ performance, as it needs to be more focused on sheer speed than grip since there’s plenty of the latter.
Taking into account a better PI calculation method (and the current D500 performance being in the ballpark of Forza Motorsport 4’s E class), here is my proposed PI class division for Forza Horizon 6:
F 100-200
E 201-300
D 301-400
C 401-500
B 501-600
A 601-675
S1 676-750
S2 751-825
R1 826-900
R2 901-950
R3 951-998
X 999