175/60 R 14 75H
175 is the
width in
mm of the
tyre tread (could be 100 up to 325 for ultra-sporty tyres)
60 is the aspect ratio in percent. In this case the tyre height (from rim to tread) is 60 percent of the width (which is 175mm). That works out as 105mm. Not normally higher than 82, and can go as low as 30 for ultra-sport tyres. "low profile" means an aspect ratio below about 60 percent
R means radial construction. The alternative is Cross-ply or bias ply
14 is the rim diameter in inches. A very small car runs on 12-inch rims, big sports cars use 18, 19, or even 20-inch rims to make maximum space for big brakes. The biggest specialist rims are now 22 inches--as big as a truck tyre rim!
75 is the Load Index and indicates the maximum load that should be applied to the tyre when driven at maximum speed. In this case 75 means 387 kg. For all but heavy trucks, this is not usually a problem, but you can find load ratings here:
http://www.tyres-online.co.uk/techinfo/load_indices.asp
H is the speed rating. This is the maximum speed the tyre should ever be driven. This is the area where you have most choice. Higher speed ratings mean higher prices, and often, shorter life.
N 140 kph / 87 mph
P 150kph / 93 mph
Q 160 kph /99 mph
R 170 kph / 106 mph
S 180 kph / 112 mph
T 190 kph / 118 mph
H 210 kph / 130 mph
V 240 kph / 149 mph
W 270 kph / 168 mph
Y 300 kph / 186 mph
Z over 300 kph
other marking include M+S for Mud and Snow (winter tyres)