@WYCorp Indeed i was right. Did the test now, and fuel_cons.ini for RSS f1 '90 is of for more than 30%, and what is worse, it's off in the wrong direction. So when after a few laps after a race start, the AI realise they have 33% less fuel than wanted, they panic and pit. I can't believe RSS would make such an oversight. Not like them at all. Anyway I attached the excel table I use for doing this for the cars that have this problem if anybody wants it (rename .txt to.xlsx and use it freely). I do 3 tests: Silverstone, Spa and Magny Cours (three very different tracks to get the average value).
Change the fuel_cons.ini of the RSS '90 from:
[FUEL_EVAL]
KM_PER_LITER=2.1
to
[FUEL_EVAL]
KM_PER_LITER=1.582773194