small list about Forza:
- only fixed-ratio center differentials are simulated, no viscous, no active systems like in a Lancer or Impreza for example
- ground effect aero effects aren't simulated (stronger the closer the car bottom is to the surface)
- ABS and TC is non-adjustable (it's just ON/OFF and the same slip ratio starting point for all cars if set to ON)
- cockpit adjustable brake balance not present
- cockput adjustable anti-roll bars not present
- brake balance adjustability in the garage is tied to having carbon-ceramic brakes, older race cars are non-adjustable entirely in FM
- no correct caster, camber toe settings taken from IRL production cars (edit: spring rates are also not original, just what feels good and believable)
- dampers only have one setting, no "fast bump" like modern race car dampers have
- can't flash the lights for overtaking blue-flagged cars
- no simulation of torque vectoring differentials
- no simulation of brake-disc heat warming up the tires
- no brake fade or overheating brake discs
- no engine cooling simulation
- no engine damage from over-revving or overuse of high-end revving
- no adjustable turbo pressure in race cars (for many 70s and 80s car really important)
- no passive or active rear wheel steering in cars that have it
- no manual DRS use
- incorrect simulation of hybrid drive systems
- no battery charge with kinetic energy recovery
- no settings for recovery mode
- no distinction between gasoline motor enhancing and wheel-driving battery power use
- doesn't apply battery power to the correct axle if different from standard driven axle
I'm sure I could come up with more and for the record, Assetto Corsa for example simulates all of the above and most of it pretty well. Also, that was only the car-simulation, didn't even go in the general simulation aspects like flat spotting, correct DRS zones and rules, Push-to-pass (with rules), wind direction, air density with temperature... actual sims do all of those.