How much Fuel is too much Fuel?

Does a full fuel tank waste cash? Is there an optimum level to which you should fill your car's petrol tank so it doesn't just use the excess energy simply to carry the petrol around? Do vehicle manufacturers make the capacity of the petrol tank the perfect size with this in mind? Plus, passenger jets arrive cold, but spacecraft burn up - when does wind chill give way to frictional heating? Like this podcast? Please help us by supporting the Naked Scientists