Road salt, mud, pollen, bird droppings, dust and many other things get stuck and erode the car parts. Particularly road salt is a true enemy and it causes rust and corrosion in the undercarriage if it is not regularly washed offs. If possible, flush the undercarriage with a water hose during salt season. It is a delicate balance, how often you should wash your car, because too much wash will tear the paintwork and it is not very eco-friendly. We recommend once a month.