BMW X3 Owners Manual > Wheels and tires: Tire identification marks
Tire size
245/45 R 18 96 Y
245: nominal width in mm
45: aspect ratio in %
R: radial tire code
18: rim diameter in inches
96: load rating, not for ZR tires
Y: speed rating, before the R on ZR tires
Speed letter
Q = up to 100 mph, 160 km/h
R = up to 106 mph, 170 km/h
S = up to 112 mph, 180 ...