Had a MK3 TDI once and as i put mudflaps on it and as i was doing alot of miles noticed my mpg changed from 55 to 50 . They also didn't make any difference to the crap it threw onto the car and if anything made the rear screen dirtier . Took them off and the mpg went back to 55 . I wouldn't do it to any modern day car , they are not needed . Be assured if they were cars would be sold with them .