Width
The first number or second letter in a tire size represents the nominal width. Width is measured in a straight line from the furthest point on one sidewall, across the tread, to the furthest point on the opposite sidewall. If there is any question whether or not a larger than OEM tire will fit your bike, you're encouraged to call Tech Service. The different size numbering systems specify widths in different measurements. You can view a width cross reference table below.
Aspect Ratio
Aspect Ratios indicate a tires cross-sectional profile. The smaller the number, the lower the profile. It expresses the height to width ratio as a percent. A 90 aspect ratio means the tire's cross sectional height is 90% of it's width. The aspect ratio appears immediately after the width in the Metric, Alpha and Low Profile Inch numbering systems.
Speed Rating
Speed Ratings are internationally recognized maximum speeds at which the tire may be used with maximum load when the maximum listed inflation pressure is used. Maximum loads and inflation pressures are found on the sidewalls of the tires. Speed ratings are coded by a letter, which appears directly after the width, aspect ratio, or as part of a three digit Load/Speed Index, found on the tire directly after the complete size designation.
Tire Construction
The Tire Construction, when included in the size numbering, is listed after the speed rating. The two options for tire construction are Belted (B) or Radial (R). A belted tire has fiberglass, Kevlar, or aramid fiber belts for added strength and load capacity, however not all belted tires will have the B designation. If a tire does not have the Radial (R) designation, it is a bias-ply tire.
Rim Diameter
Rim diameter is the diameter of the rim/wheel on which the tire will be mounted, in inches.
Additional Information
Some tires may have additional information in their size, for example WW, meaning it's a white wall tire. If the size is followed by TT, it means that it is a tube type tire, which requires an inner air tube. TL means it's a tubeless tire. Others may have M/C at the end of the size, which simply means it is a motorcycle tire.
Tire Size Numbering Systems
There are four different motorcycle tire size systems currently in use.The systems can have up to the five parts listed above. The different systems are:
