Tire Markings

Ever wondered what the gibberish printed on the side of your brand new Yokohamas actually means? Well, here's the lowdown! Take note of the fact that the units used are all over the place. Width is in millimetres, diameter is in inches, and aspect ratio is a percentage! Whoever designed the system wants shooting!!!

Format:

(Code) ( Width) / (Aspect) (Speed) (Construction) (Size)
For example, on a 13" wheel Mini you may well see something like P 175 / 50 VR 13

Code:

P = Passenger
LT = Light truck
T = Temporary
LTP = Light truck, personal use

Width:

Width at widest point, sidewall to sidewall, in millimeters

Aspect Ratio:

Tire height in millimetres, measured tread to bead, divided by width above, multiplied by one hundred.

Speed ratings:

(The maximum speed the tire can safely maintain at its maximum load rating)

Q - 100 mph 160kph
R - 106 mph 170kph
S - 112 mph 180kph
T - 118 mph 190kph
U - 124 mph 200kph
H - 130 mph 210kph
V - 149 mph 240kph
W - 168 mph 270kph
Z - more than 168 mph 270kph
Construction:
R - Radial ply
B - Bias belted
D - Diagonal bias

Size:

The diameter of the wheel the tire is designed to be mounted on, in inches.

Other information:

Maximum Air Pressure - This is the max pressure the tire is designed to hold (note this is more than the recommended inflation pressure)
Maximum Load - Weight the tire can support
Load Index - A code that indicates the maximum weight the tire can carry at its speed indicated by its speed rating
Construction - Tells the number and type of plies used in the construction of the tread and sidewall
DOT Serial Number - Identifies the plant, manufacturer, and date of production
Tread Wear Index - A rating of the tire's resistance to wear. 100 is the reference. A 250 rating indicates 2.5 times the wear resistance of the reference tire. This number cannot be accurately translated to mileage.
Traction Index - A rating of the tire's ability to stop on wet pavement. There are three grades, A, B, and C, with A being the best. This index does not reflect the tire's traction performance on dry, snowy, or icy pavement.
Temperature Index - A rating of the tire's ability to dissipate and resist heat. There are three grades, A, B, and C, with A being the best.

source :minifinity tech page