re drag coefficients in article apr wdl loral com gwm spl spl loral com gary w mahan writes could someone explain how to make sense of drag coefficients i e cd mentioned in magazines i understand that lower numbers signify better aerodynamics but what does this mean in the real world is there a way to calculate new top speeds assuming the car is not rev limited at top speed or mileage benefits if a identical car had the cd reduced from to i don t remember the formula s off hand as it has been awhile since i took aerodynamics and haven t used the stuff since the cd is related to the drag force which is what effects top speed and fuel consumption when the drag force on the car or aircraft is greater than what the vehicle s engine can overcome it has reached its top speed autos of course also have to overcome rolling resistance since drag opposes the vehicle s motion the engine must make up for that by burning more fuel anyway since the geometery of an auto is rather complex the drag pressure coeffiecent etc is either found experimentaly or using a numerical method anyway for flow around a cylinder the drag coeff is cd d q r where d is the drag force q the flow velocity and r is the radius of the clyinder to get a rough very rough estimate you can set r at the car s width q at the car s speed and knowing the cd find the drag force that the car would need to overcome bp
