The arrangement of holes surrounding the center of the wheel that allow it to be bolted to the hub. Differences in vehicle make and model determine how many holes there are and the diameter between them. This is the most important information to know about your car when replacing your existing wheels, as only one bolt pattern will work on any given vehicle.

 

The distance from the surface of the wheel mounting pad to the outer edge of the wheel flange. Back spacing is typically different for cars than it is for trucks. It is often important to know what backspacing your vehicle can accomodate when shopping for aftermarket wheel and tire packages.

 

The distance from the vertical centerline axis of the wheel to the wheel mounting pad. Offset is also an important factor to consider when buying an aftermarket wheel. When combined with back spacing, an extreme positive or negative offset can cause problems with wheel fitment or tire rub.

To find offset reference the width and the backspacing of your wheel on the table above.

 

The inside diameter of the center hole in the wheel. Certain cars have a raised hub center and their factory wheels are machined to fit snugly around it as a more stable method of wheel centering. Such wheels are called 'hubcentric' and will not fit on certain other vehicles with larger hub diameters.

 

 

 

The letter or letters preceding the numbered size codes indicate the type of vehicle and recommended usage for the tire. Some common service types are:

P - Passenger. Used primarily on cars, minivans, SUV's and light trucks

LT - Light Truck. Used primarily on light to medium duty trucks, SUV's and ORV's

T - Temporary. Indicates a tire that is to be used only as a spare until a failed tire can be replaced.

C- Commercial. Indicates a tire that is rated for vehicle that carry heavy loads. (see Load Range below)

ST - Special Trailer. Used only on boat, car, or utility trailers.

 

A three digit number that represents the total width of a mounted, inflated tire at it's widest point from the outer sidewall to the inner sidewall. Using the metric system, this dimension is measured in millimeters (mm).

 

A two digit number following the section width that represents the height of a tires sidewall as a percentage of the section width. In the example above the tire has a section width of 205 mm and the sidewall is 70% as tall as the tire itself is wide. The combination of the sidewall aspect ratio and the section width are the most important determining factors of the actual dimensions of the tire.

 

The letter or letters following the sidewall aspect ratio indicate the type of materials that make up the tire itself and the speeds at which the tire will safely perform. Most tires on the road today have a 'radial' construction, hence the letter 'R'. Some tires are rated with the letters 'D' or 'B' to signify diagonal (bias-ply) or belted construction. A tires speed rating indicates the maximum speed at which a specific tire can operate safely without losing grip on the road or coming apart due to excessive centrifugal forces.

 

The final letter in the sequence represents the total diameter of the tires mounting bead. This measurement must match exactly the total diameter of the wheel.