Definition of terms for tires and loading

Tire ply composition and material used

Describes the number of layers or the number of rubber-coated belts in the tread and the sidewall of the tire. These are made of steel, nylon, polyester and other materials.

Bar

Metric unit for tire pressure.

14.5038 pounds per square inch (psi) and 100 kilopascals (kPa) are the equivalent of 1 bar.

DOT (Department of Transportation)

DOT marked tires fulfill the requirements of the United States Department of Transportation.

Normal occupant weight

The number of occupants for which the vehicle is designed multiplied by 68 kilograms (150 lbs).

Uniform Tire Quality Grading Standards

A uniform standard to grade the quality of tires with regards to tread quality, tire traction and temperature characteristics. Ratings are determined by tire manufacturers using U.S.

government testing procedures. The ratings are molded into the sidewall of the tire.

Recommended tire pressure

The Tire and Loading Information placard contains the recommended tire pressures for cold tires on a fully loaded vehicle and for the maximum permissible vehicle speed.

The tire pressure table contains the recommended pressures for cold tires for various operating conditions, i.e. differing load and speed conditions.

Increased vehicle weight due to optional equipment

This is the combined weight of all standard and optional equipment available for the vehicle, regardless of whether it is actually installed on the vehicle or not.

Rim

This is the part of the wheel on which the tire is mounted.

GAWR (Gross Axle Weight Rating)

The GAWR is the maximum gross axle weight rating. The actual load on an axle must never exceed the gross axle weight rating. The gross axle weight rating can be found on the vehicle identification plate on the B-pillar on the driver's side.

Speed rating

The speed rating is part of the tire identification. It specifies the speed range for which the tire is approved.

GTW (Gross Trailer Weight

The GTW is the weight of a trailer including the weight of the load, luggage, accessories etc. on the trailer.

GVW (Gross Vehicle Weight)

The gross vehicle weight includes the weight of the vehicle including fuel, tools, the spare wheel, accessories installed, occupants, luggage and the drawbar noseweight, if applicable. The gross vehicle weight must not exceed the gross vehicle weight rating GVWR as specified on the vehicle identification plate on the B-pillar on the driver's side.

GVWR (Gross Vehicle Weight Rating)

The GVWR is the maximum permissible gross weight of a fully loaded vehicle (the weight of the vehicle including all accessories, occupants, fuel, luggage and the drawbar noseweight, if applicable). The gross vehicle weight rating is specified on the vehicle identification plate on the B-pillar on the driver's side.

Maximum loaded vehicle weigh

The maximum weight is the sum of: • the curb weight of the vehicle • the weight of the accessories • the load limit • the weight of the factory installed optional equipment

Kilopascal (kPa)

Metric unit for tire pressure. 6.9 kPa corresponds to 1 psi. Another unit for tire pressure is bar. 100 kilopascals (kPa) are the equivalent of 1 bar.

Load index

In addition to the load-bearing index, the load index may also be imprinted on the sidewall of the tire. This specifies the load-bearing capacity more precisely.

Curb weig

The weight of a vehicle with standard equipment including the maximum capacity of fuel, oil and coolant. It also includes the airconditioning system and optional equipment if these are installed in the vehicle, but does not include passengers or luggage.

Maximum load rating

The maximum tire load is the maximum permissible weight in kilograms or lbs for which a tire is approved.

Maximum permissible tire pressure

Maximum permissible tire pressure for one tire.

Maximum load on one tire

Maximum load on one tire. This is calculated by dividing the maximum axle load of one axle by two.

PSI (pounds per square inch)

A standard unit of measure for tire pressure.

Aspect ratio

Relationship between tire height and tire width in percent.

Tire pressure

This is pressure inside the tire applying an outward force to each square inch of the tire's surface. The tire pressure is specified in pounds per square inch (psi), in kilopascal (kPa) or in bar. The tire pressure should only be corrected when the tires are cold.

Cold tire pressure

The tires are cold:
• if the vehicle has been parked without direct sunlight on the tires for at least three hours and
• if the vehicle has not been driven further than 1 mile (1.6 km)

Tread

The part of the tire that comes into contact with the road.

Bead

The tire bead ensures that the tire sits securely on the wheel. There are several steel wires in the bead to prevent the tire from coming loose from the wheel rim.

Sidewall

The part of the tire between the tread and the bead.

Weight of optional extras

The combined weight of those optional extras that weigh more than the replaced standard parts and more than 2.3 kg (5 lbs). These optional extras, such as high-performance brakes, level control, a roof rack or a highperformance battery, are not included in the curb weight and the weight of the accessories.

TIN (Tire Identification Number)

This is a unique identifier which can be used by a tire manufacturer to identify tires, for example for a product recall, and thus identify the purchasers. The TIN is made up of the manufacturer's identity code, tire size, tire type code and the manufacturing date.

Load bearing index

The load bearing index (also load index) is a code that contains the maximum load bearing capacity of a tire.

Traction

Traction is the result of friction between the tires and the road surface.

TWR (Tongue Weight Rating)

The TWR specifies the maximum permissible weight that the ball coupling of the trailer tow hitch can support.

Treadwear indicators

Narrow bars (tread wear bars) that are distributed over the tire tread. If the tire tread is level with the bars, the wear limit of 1/16 in (1.6 mm) has been reached.

Occupant distribution

The distribution of occupants in a vehicle at their designated seating positions.

Total load limit

Nominal load and luggage load plus 150 lbs (68 kg) multiplied by the number of seats in the vehicle.