There are two sizes of tires used on a Mercedes ML350: 255/50-19 and 265/45-20. The tires sizes vary according to what type of wheels were originally purchased for the vehicle, or the ones that are currently mounted on the car.
Mercedes ML350 models were available in several trim levels. The basic models featured 19-inch wheels used 255/50-19 tires. Other sizes can also be installed as long as there is space between the wheel and chassis.
More luxurious trim models included 20-inch wheels, which featured the 265/45-20 tires. The only other difference between both sets of tires, besides its size, is the width.