Example: 255/55 R 19 107 V
255: nominal width in mm
55: aspect ratio in %
R: radial tire code
19: rim diameter in inches
107: load rating, not for ZR tires
V: speed rating, before the R on ZR tires

Speed letter

Q = up to 100 mph/160 km/h
T = up to 118 mph/190 km/h
H = up to 131 mph/210 km/h
V = up to 150 mph/240 km/h
W = up to 167 mph/270 km/h
Y = up to 186 mph/300 km/h