@Nellix82 Who are the "experts" you are hoping to hear replies from? I know Mariohomoh used to geek out about the whole setup thing, but I think he kind of gave up and moved on because he realized how basic the engine was. Which leads me to the primary point I've been trying to make to you in our conversations. The game uses a fairly basic engine, it's not calculating how much fuel your burning every second and adjusting some weight coefficient to determine your new handling modifier.
Yes, there are probably break points where things get recalculated like 80% fuel 60% etc. just as tyre wear seems to have break points where you hit a cliff, but the game isn't dynamically recalculating every aspect of your car on the fly. The series was built with the average gamer in mind so they could pick up and play without having the spend hours tuning their car just to keep up with Logan and the Alpines while they themselves are driving a Red Bull.