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Motorcycle tire size is fundamental because bikes generally work best with the manufacturer's intended tire size. There are occasions when a tire that is not the factory-recommended size can be used, but we always suggest sticking to the manufacturer's specs. That way you ensure proper clearances between components, optimal handling and appropriate load and speed ratings for the build of your bike.
Three designations exist that you might encounter regarding tire size - Metric, Alphabetical and Inch. Below is a brief outline of each.
180 - Width (in millimeters)
55 - Aspect Ratio (height of the sidewall/width of tread multiplied by 100. Expressed as a percentage)
R - Construction (R-Radial, B-Bias Belted, No Letter - Bias)
17 - Rim Diameter (in inches)K
73 - Load Index (maximum load carrying capacity at maximum pressure - see chart for conversion)
W - Speed Rating (maximim speed under recommended load capacity - see chart for conversion)
M- Motorcycle Code (Simply indicating the tire is built for a motorcycle)
T - Tire Width Code (Letters represent inch measurements - check chart for conversion)
90 - Aspect Ratio (%)
B - Construction (R-Radial, B-Bias Belted, No Letter - Bias)
16 - Rim Diameter (in inches)
74 - Load Index (maximum load carrying capacity at maximum pressure - see chart for conversion)
H - Speed Rating (maximum speed under recommended load capacity - see chart for conversion)
3.00 - Section Width (in inches)
21 - Rim diameter (in inches)
4PR - Casing Strength (Ply Rating)
A Bias Belted tire utilizes ply cords that extend diagonally from bead to bead relative to the centerline and a stabilizer belt across the width of the tire.
Advantages: This type of tire provides a smooth ride that is similar to the bias tire, but lessens rolling resistance due to belts increasing tread stiffness. The plies and belts are at different angles, which improves performance that compare to non-belted bias tires.
Bias tires typically have the ply cords that extend diagonally from bead to bead at a range of 30 to 60 degree angles from the centerline. Each successive ply is laid at an opposing angle, forming a criss-cross pattern.
Advantages: The design allows the entire tire body to flex easily, giving a comfortable ride on rough surfaces.
Radial constructed tires utilize both ply and breaker (or belt) cords. The Ply cords extend from bead to bead at approximately 90 degree angle to the centerline of the tire. The breaker (or belt) cords are placed on top of the ply cords across the width of the tire.
Advantages: Adding breaker (or belt) cords results in a stiffer carcass which helps provide a longer tread and tire life, better steering control and handling, overall smoother ride and comfort, and higher tread puncture resistance.
The load rating indicates the maximum weight that can be carried safely by the tire when inflated to the maximum recommended tire pressure. Take this one seriously and don't overload your tires!
The speed rating is the maximum speed the manufacturer determines a tire can manage when at its load capacity.
Motorcycle tires, when properly stored and cared for, have a long service life. When stored properly, tires from 5-7 years old can retain all the chemical and physical properties of a brand new tire. Most manufacturers recommend tires 10 years or older to be replaced by a new set, regardless of storage or usage circumstances.
The production date is found on the tire sidewall at the end of the series of letters and numbers starting with DOT. Tires produced after 1999 utilize a code in which the final four digits of this series provide a week and year of production. For example, 1916 is the 19th week of 2016.
Tires need to be stored in clean and dry environment that is dark and well ventilated. If tires are on the rim and stacked, they need to be restacked every four weeks. Hanging tires that are on rims is preferred. Tires without rims must not be stacked or hung up, but stored standing upright and rotated every four weeks. This is to ensure the tires retain their original shape.
Numerous other issues can affect the life of a stored tire, from chemicals stored in the vicinity, light or temperature fluctuations and the like.
All tires need to be checked regularly. For tires in use, tread depth should not be less than 2mm. There should be no cracks or deformaties in the tire and valve-stems need to be in good condition. Rims need to be in good condition as well.
Riders Domain recommends that all tires be inflated to the manufacturer's recommended tire pressure for the expected conditions and loads. Tire pressures should be measured when the tires are cold.
When you get a set of new tires know that the external surface will be quite smooth owing to production processes. It is recommended that riders avoid sudden braking and extreme lean angles during the first 100 miles or so, until the surface is sufficiently scrubbed in.