Jon
So what I'm gathering from this is one fuel.economy is 50 it's basically not worth doing any more and once tyre economy is anything over 10 it's useless?
TE about yes, although it wouldn't hurt if you go above 20 but that should be the case even if it's the CDs weakness anyway. Still I'd prefer a CD with Cooling or Reliability as weakness instead if I can get one.
Fuel no, it's usefull beyond that. Although it's of note that more is not always better. For example my car needs 1.97 litres per lap and is planned to do 12 lap stints. So I'd set it up with 24 litres which leaves me with 0.36 litres at the end. Not perfect but pretty good. But now I decide to 'improve' FE a bit and the consumption wents to 1.93 litres per lap. I still have to fill up 24 litres for 12 laps, though, but have now 0.84 litres remaining. That's 0.48 litres more fuel that's nothing more than extra ballast. So by doing that I made my car worse, especially bad if it's the case for the last lap of the race when I want every advantage.