Luke
My suggestion is like ideal setup. Could use tokens to buy ideal fuel for race. It could be apart of ideal setup or a separate thing.
I don’t think there is an ideal fuel you can put in your car. It depends on the track temp and the strategy you have, if you have soft tyres then it will be easier to warm them and require less fuel, but if you go with mediums and hards, then it will take more fuel. Similarly for track temp, this can be considered by the code, but again will it consider futuristic track at the time of race (which might not be possible or realistic as weather is always unpredictable) or the track temp of your practice run.