Someone here asked how to dial-in Adaptive AI difficulty, and then deleted their right as I responded. Posting my reply here because I'm mad I typed it out for nothing lol.
The freshly-deleted thread is here.
My reply:
The Adaptive AI in raceroom doesn't adjust during the race - rather, it's set before the race even starts.
So for any given class+track combination, the difficulty that Adaptive AI chooses is based on the average of your 10 best laps on that track.
Meaning, you will have to spend a race getting a few good laps in (usually 5 is the minimum to get the perfect difficulty), and then you will have to either finish the race, or retired to the Garage, and then clicking Finish Race (as just doing 5 laps and then Quitting will not record the lap times).
Afterwards, when you try the car+track combo again, the AI will be tuned to the average of your recorded lap times.
CAVEATS / NOTES:
The game can use your times from other tracks you raced in the same class, so sometimes it can guess the right difficulty without first "trainiing" it.
The game also records the AI's average laptimes too, to help select the right difficulty. So be careful if you cause a pileup, and make the AI finish their laps like 30 seconds late!
It doesn't matter if you use Timed or Lapped modes when recording your times.
It doesn't matter, when you record your laps, how ahead or behind you are from the AI. All the game cares about is the average of YOUR top-10 best laptimes.
I said "your top ten best lap times", but the game does eventually evict stale laptime entries. So if you record 10 laps getting around 30s per lap, start a new race, and record 3 really bad laps @ 40s each, it will evict 3 entries, so that 7 entries are from your 1st race, and 3 are from your 2nd race with the really bad laptimes.
Hope this helps!
TL;DR: Start a race, and record 5 good laps for a car+track combo, then finish the race or retire to the garage. Next time you launch that car+track combo from the main menu, it'll select a suitable difficulty.