User:N0NB/Sandbox

Motorcycle tires are available in a large selection of sizes and profiles to fit different motorcycles and to suit various purposes. While looking through a catalog of tires, a difference of size designations may be encountered between the catalog and the tires on the bike or listed in the motorcycle owners manual. Conversion is easy once the coding systems are understood.

Designation codes
Three common code systems for designating motorcycle tires exist. Modern tires utilize a metric coding system where the tire dimension is described as the cross-sectional width expressed in millimeters followed by an integer that describes the aspect ratio (tire height to its width) followed by the rim diameter expressed in inches.

In a similar fashion, two older coding system use either an alpha code or inches to describe the cross-sectional width of the tire. The alpha coding also includes a two digit integer to designate the aspect ratio of the tire. A tire expressed in inches may or may not include an aspect ratio designator. In either system, the width is followed by the rim size expressed in inches.

After the rim size, the tire code may also include the speed rating, load rating, ply rating, and tube or tubeless designators or this information may be found elsewhere on the tire sidewall.

Converting Street Tire Codes
It is common for the front tire of a motorcycle to be narrower and/or have a different rim size than the rear tire. Despite this difference, the coding system remains the same for front and rear tires.

N.B. These conversions are indicative of the relationship to common sizes. Consult the tire manufacturer's fitting data or the motorcycle's owners manual for proper tire size selection.

Speed Ratings
A single letter is used to designate the speed rating of the tire. While this letter may be a duplicate of the second letter of the alpha code, it is separate and distinct.

N.B. Dunlop states, "For tires having a maximum speed capability above 149 mph, a Z must appear in the size designation. Consult tire manufacturer for maximum speed when there is no service description."

Load Range Index
The load range index may be expressed as a two-digit value or simply be stated on the tire sidewall in kilograms and pounds. This is the maximum load at the maximum tire pressure the tire can safely carry.

N.B. Despite the tire load index, the motorcycle should not be loaded greater than the gross vehicle weight specified in the motorcycle owners manual.

Other Markings
Besides the codes already described, several more coded markings can be found on the tire sidewall.

Construction
Tire construction falls into one of two categories--radial, R, and bias ply, B. Consult the motorcycle's owners manual for the type of tire that should be mounted.

Date Code
The date code consists of four digits (three for tires manufactured before 2000) where the first two digits designate the week of the year and the last two digits (one if made prior to 2000) designate the year. 1407 would indicate the first week of April 2007. The date code is the suffix of a block of characters that includes the USDOT identification number.

Pressure
The maximum tire pressure is displayed in Pounds per Square Inch, PSI, or kilopascals, [Pascal_(unit)|kPa]. The motorcycle's owners manual should be consulted for the recommended tire pressures for vaying load weights.

Other
The tire may also include other markings and symbols that are important for mounting the tire and balancing the wheel assembly.

Tube/Tubeless
The words "Tube Type" or "Tubeless" may appear on the tire sidewall. Alternately, these may be designated with the letters TT or TL respectively. It is important that the proper type of tire be mounted as the wheel rims are designed for one type or the other. The motorcycle's owners manual will specify which type is to be mounted.

Balance Mark
Manufacturers often pre-balance the tire and will mark the spot with a painted dot (or dots) on the tire sidewall where the valve stem should line up.

Rotational Marks
The tread design on a motorcycle tire is designed to rotate one way. Correct treat orientation is required to channel water away from the contact patch to prevent hydro-planing (a condition where water builds up between the tire and roadway and contact with the roadway is lost). Proper rotation is required to prevent tire damage due to braking or acceleration due to the tire's construction process.

Wear indicators
Tire wear indicators are small bars in the the tread that indicate the minimum safe tread depth. Their position may be indicated on the tire sidewall with triangles or the letters TWI.

Summary
Much information about the tire is contained on the tire sidewall. Besides assuring the correct fit for the motorcycle, important safety information is contained in the various letter and digit codes. Understanding the codes will allow the motorcyclist to avoid overloading the tires or operating them beyond the rated speed. When the tire is mounted to the rim, correct rotational direction must be maintained and attention to the balance marks will aid in balancing the wheel assembly.

During the life of the tire, the motorcyclist must be aware of the maximum recommended pressure to inflate the tire as well as the tire wear indicators so the tire can be replaced before the tread is worn beyond a safe level.

Safe operation of a motorcycle depends on good tires as they provide the only means of controlling the motorcycle on the road.