Useful stuff, thanks Dean0
EG : 180/55 ZR 17 M/C (73W) TL

180: tyre section nominal width [mm]
55: tyre aspect ratio [%]
ZR: tyre construction type
17: rim diameter [inches]
M/C: tyre for motorcycle only
73: load index code
W: speed index code
TL: tubeless tyre

Speed index codes ( Mph ratings )

L = 75
M = 81
P = 93
Q = 100
R = 106
S = 113
T = 118
U = 124
H = 130
V = 130
W = 168
(W) = 168+ ("C" rated)
Z = 150