To my knowledge, Forza games have been relying on mostly the same PI calculation method since at least Forza Motorsport 5 - an AI driver takes the car around all tracks in the game and based on the average lap time the game calculates its performance. The caveat to this is that this AI driver isn’t very skilled and is apparently prone to losing control of the car, which may be true considering that sometimes telemetry data in the upgrade shop shows that the car couldn’t reach a certain speed. Now in Forza Horizon 6 I believe this should be fixed.
The AI driver that “tests” the cars should be skilled enough to avoid losing control of the car, no matter its grip, which would require it to drive slower at times yet end up being faster. This would ensure a more accurate PI calculation which would nerf powerbuilds and possibly buff some slower cars. If possible, tuning should also impact PI, as it is often crucial to make a car perform at all.
As for Track Rating, this would be similar to “Recommended Cars” in Horizon 5 pre-race car selection, but taken to a higher level - a separate PI. When upgrading a car, the player would have the option to select a track for which the tune will be designed, and a separate PI number would then show up to accurately display how the car will perform on that track. Better yet, if tuning cannot impact the base PI then it could impact the Track Rating, provided an additional “track run” will take place with each adjustment.
This video by Giron228 opened my eyes to even more issues with the current PI calculation system: I somehow glanced over the fact that the game does not calculate the power of an engine beyond what’s described as “set gearshift point”, which is usually well below the maximum RPM it can achieve, and also just how much gear shift time impacts the performance. The incomplete dyno graph allows for making some ridiculous builds that end up outperforming everything because of how much power is hidden from the game’s actual power calculation, and the use of automatic transmission by the bot that calculates the PI causes a lot of the power output to be simply drowned by gear shift times.
All of this means that, on top of giving the calculating AI as much skill as possible so that it is capable of handling any car with no assists whatsoever, that AI driver must also be using manual with clutch on cars that have non-instant shift times (I’m sure there’s a way to calculate that), and must utilize the full power curve of the engine, even if it goes well over 1000 RPM beyond the redline.
I highly recommend everyone to watch this video to get more of an insight as to how PI calculation has been working in Forza since at least FM3 if not earlier.
