When painting a car, it can be hard to remember to protect every part from overspray. Tires are often left uncovered since they don't seem to be a major part of the car's surface. Overspray from paint and primer can get all over the rubber on the tires. Most of the paint may come off over long periods of time, but it you want to remove the paint overspray from the rubber immediately, it will take some work.
Pour paint thinner onto a towel and then wipe the towel over the paint overspray. Make sure the towel is soaked with thinner. Don't pour the thinner directly on the tires or you risk getting thinner on the rims or the surrounding painted surfaces of the car. You need enough thinner to soak the paint overspray on the tires only. Allow it to soak for five minutes.
Use a red scuff pad from an auto parts store to scrub the paint overspray. Red scuff pads are the equivalent to a fine grit sandpaper but won't fall apart when scrubbing the rubber tires. Scrub until all the overspray is gone.
Wash the tires and wheels with car wash soap and water. This removes any remaining paint thinner and overspray. Don't use dish liquid, which can cause the rubber to dry out prematurely. Rinse the tires and wheels completely with a hose or clean water.
Paint thinner is toxic and harmful if the fumes are inhaled. Use paint thinner in an open, well-ventilated area.