Freshly cleaned and waxed vehicles are said to get better fuel economy because they have less wind resistance than a vehicle coated with grime. The theory is that the smooth surface is more aerodynamic and reduces air resistance and drag.
Some say cleaning and waxing your car can add up to a 7% difference in fuel economy, but others say the claim is purely a myth because the theory only applies to airplanes. This stance holds that cars don’t travel fast enough for layers of dirt to make a difference in wind resistance, but jet planes do.
Whether the theory is true or not, I guess there’s a lot to be said for a clean, shiny car – especially if it’s seen newer days!