Fuel is weight
Every car gets heavier as you fill it. A full tank makes it slower off the line, slower to stop and lower at top speed, and it costs grip in the corners. As the race goes on and the fuel burns away, the car gets quicker lap by lap.
Every race needs at least one stop, because a full tank never lasts the whole distance. One stop means a heavy car for longer stints; two stops mean a light car but another trip down the pit lane. On some circuits one stop is faster, on others two, and each car prefers a different plan.














