How to read my tire

You can find all the basic details about a tire by reading the information on the sidewall.

255 = Tire Width

Measured in millimeters from sidewall to sidewall

55 = Aspect Ratio

This is the ration of the height of the tire’s cross-section height to its width. E.g. 55 means that the height is equal to 55% of the tires’s width

R = Construction

The R stands for radial and means the body ply cords - layers of fabric that make up the body of the tire and run radially across it from bead to bead. The letter B indicates that the tire is of bias construction, meaning that the body ply cords run diagonally across the tire from bead to bead, with the ply layers alternating in direction to reinforce one another.

18 = Wheel Diameter

The width of the wheel from one end to the other. The diameter is displayed in inches.This tells you on which rim diameter your tire can be mounted

91 = Load Index

This is an index (not a direct indication of the load) indicating the maximum load that the tire can support when properly inflated.

Y = Speed Symbol

Shows the maximum service speed for a tire. 
L: 120 km/h
M: 130 km/h
N: 140 km/h
P: 150 km/h
Q: 160 km/h
R: 170 km/h
S: 180 km/h
T: 190 km/h
U: 200 km/h
H: 210 km/h
V: 240 km/h
W: 270 km/h
Y: 300 km/h
This rating relates only to tire speed capability, and is NOT a recommendation to exceed legally posted speed limits which must always be respected.