If it's anything like the F1 2012, then you will have to switch to a lean fuel mix at some time during the race. You will not reach the end if you leave it on Standard Mix, or use Rich Mix often.
There is also an option carried over from F1 2012, to set your fuel strategy before the race. So you can carry more or less fuel, which will determine what mixes you use.
Extra fuel = More time at Standard or Rich mix, but slower lap times because of the weight
Less Fuel = More time using the Lean mix, but faster lap time because of weight.
I think they have name for these Strategies e.g Conservative, Standard. I am not sure of the names, as I haven't done a career race yet, just the scenarios.
