POLYURETHANE TIRE SIDEWALLS

A pneumatic tire having polyurethane in the surface exposed at the sidewall is coated with a colored polyurethane elastomeric coating by (1) applying to the sidewall surface a colored coating composition comprising a dye and/or pigment, an elastomeric NCO-terminated polyurethane prepolymer and a curing agent therefor, wherein the prepolymer is formed from a substantially satured hydroxy-terminated diol having a molecular weight of 500 to 10,000 or higher and a substantially saturated aliphatic diisocyanate, the mol ratio of the diisocyanate to the diol being 1.2:1 to 2.2:1, the prepolymer having a molecular weight over 2,500 when a blocked diamine is used as curing agent, and (2) heating the coated surface to cause the NCO-terminated polyurethane prepolymer to react with free -OH and -NH in the surface of the tire. The resulting coating adheres so firmly to the sidewall surface that when the tire mounted on a rim and inflated to 24 psi, is tested against a flat large wheel surface at 50 mph., and the pressure of the tire against the wheel is increased to 200 percent of the rated load, as the test is run until the tire fails, the coating remains in place and does not crack.