2011 Mercedes R-Class Owner's Manual - Page 339

Tire labeling Tire size designation, load-bearing capacity and speed index calculated by dividing the tire width by the tire height. Tire code: tire code = specifies the tire type. "R" represents radial tires. "D" represents diagonal tires, "B" represents diagonal radial tires. Optionally, tires with a maximum speed of over 149 mph (240 km/h) may have "ZR" in the size description depending on the manufacturer (e.g. 245/40 ZR 18). Rim diameter: rim diameter ? is the diameter of the bead seat, not the diameter of the rim flange. The rim diameter is specified in inches (in). Load bearing index: load bearing index A is a numerical code that specifies the maximum load-bearing capacity of a tire. The tire load rating must always be at least half of the GAWR of your vehicle. Otherwise, sudden tire failure may be the result which could cause an accident and/or serious injury to you or others. Always replace rims and tires with rims and tires having the same specifications (designation, manufacturer and type) as shown on the original part. 337 : Tire width ; Aspect ratio in percent = Tire code ? Rim diameter A Load bearing index B Speed index i Tire data is vehicle-specific and may deviate from the data in the example. General: depending on the manufacturer's standards, the size imprinted in the tire wall may not contain any letters or may contain one letter that precedes the size description. If there is no letter preceding the size description (as shown above): passenger vehicle tires according to European manufacturing standards. If "P" precedes the size description: passenger vehicle tires according to U.S. manufacturing standards. If "LT" precedes the size description: light truck tires according to U.S. manufacturing standards. If "T" precedes the size description: compact emergency spare wheels at high tire pressure, only for temporary use in an emergency. Tire width: tire width : shows the nominal tire width in millimeters. Aspect ratio: aspect ratio ; is relationship between tire height and tire width and is specified in percent. The aspect ratio is G Warning Do not overload the tires by exceeding the specified load limit as indicated on the Tire and Loading Information placard on the driver's door B-pillar. Overloading the tires can overheat them, possibly causing a blowout. Overloading the tires can also result in handling or steering problems, or brake failure. Example: The load bearing index 91 is equivalent to a maximum load of 1356 lbs (615 kg) that the tire can carry. For further information on the maximum tire load in kilograms and pounds, see (Y page 334). Z Tires and wheels G Warning