Car tyre basics / specifications

Good website for knowing your car tyre specifications.

http://www.bridgestoneselect.com.au/learntyres/ReadingYourTyreSize.aspx

Typical example: 165 R 13 79 T

165 - means the tyre has a nominal section width of 165 millimetres (normal width of the tyre)
R - means it has radial tyres (i.e the ply construction)
13 - means it fits a 13" diameter wheel - Rim diameter
79 - Load index
T - means it's rated for speeds up to 118mph (l90kmh).

Other common speed ratings are:

S = 113mph
T = 118mph
H = 130mph
V = 149mph
Z = Over 150mph
W = 168mph
Y = 186mph