This is not a new bug. I had this in older builds too. The fuel calculation is off by a least 50% at some tracks (GTR at Indy for instance). Looks like the AIW editor creates wrong results.
It's for all cars, but there are differences between the classes. I tested this for Nordschleife in devmode some time ago. The value calculated by the AIW editor was way to high (FuelUse=270000.000000) so I modified it (FuelUse=220000.000000) and tested the updated GT's. Nissan GTR: predicted fuel consumption (pit menu) 13.5 liter per lap - tested fuel consumption (AI) 13.7 liter per lap Nissan 370z: 12 Liter per Lap - 10,5 Liter per Lap C6r: 12 liter per lap - 13.5 liter per lap Camaro: 13 liter per lap - 11 liter per lap URD C6r: 11.5 liter per lap - 12 liter per lap
this has always been a bit of a pain for me as well. Would you know how the "trackmap" plugin gets it right compared to the ISI calculations. Unfortunately I don't have this data any more as this plugin is not 64b.
The plugin doesn't calculate it, it looks at how much you're actually using. The game's estimate doesn't adjust, so if it starts wrong it stays wrong. IMO the game needs to change in that respect. Even if you calibrate a track using a standard car, then adjust each new car's figure based on testing at a known track you'll get enough variation between different track and car types let alone different vehicle configurations/conditions (fuel load, aero settings, tyre wear, boost setting, ...) that it won't always be right. You can see this even with a plugin. Run lean for a couple of laps and the estimate will be wrong for a richer setting, for example. Seems the plugin could attempt to allow for that, and so could the game.