You may not have to but it sure makes it more funI let my Ford fiesta do the work anything above 40 mpg is good .The driver needs to reprogram his /her driving habits to obtain max fuel mileage .I've found drafting behind a greyhound bus really adds a huge amount to mpg reading .Before getting excited it's not like NASCAR drafting as you don't need to get that close to the bus to pick up a draft . (my best was 69mpg)