Ice tends to stick to a lot of things as it freezes, including many of the waxes used in car polishes and paint. But if it sticks to the polish, then the outer layer of the wax peels off easily, so the ice comes off together with a fraction of the wax. If there is no sacrificial material on the paint because dirt, grit and the like have disrupted the protective wax layer, then the ice sticks to the paint itself, and is harder to remove.

Go well,

Jon

This is because, When a car is waxed, the wax allows anything that sticks onto the car to come off easily. When the car is dirty, the wax coating is hidden. This in return causes the ice to stick onto the dirt instead of sticking directly onto the car. this becomes hard to scarpe off. But when the is a clea, ice sticks directly to the wax coating on the car thus making it easier for the ice to be scraped off easily. Moto Metal Wheels