Many people don't understand the marking numbers and letters on the sidewalls of tyre's. so here is a quick guide.

Lets look at the example 225/50R16 S

225- refers to the tyre's width in millimeters (section width)

50- refers to the aspect ratio of the tyre in a percentage form. Or put another way the size of the inner radius to the outer radius of the tyre is 50% of the section width Commonly called The profile or series of the tyre.

The "R" denotes a radial tyre which is the type of construction. prett much the only type these days.

16 - The next number is the tyre's size or diameter of the rim that should match the rim size you have. So in our example tyre, it's designed to fit on 16 inch rims, and yes it's in Inches which is different to the width of the tyre which is measured in millimeters (beats me why)

S- The last letter indicated is the tyre's speed rating, which indicates what the maximum speed that tyre should be safe to use up too. providing it's undamaged and inb good condition. The following table shows all the possible speed rating and their speeds. So our example tyre is safely rated to 180km/h or 112 mph

M = 130km/h or 81 mph

N = 140km/h or 87 mph

P = 150km/h or 93 mph

Q = 160km/h or 99 mph

R = 170km/h or 106 mph

S = 180km/h or 112 mph

T = 190km/h or 118 mph

U = 200km/h or 124 mph

H = 210km/h or 130 mph

V = 240km/h or 149 mph

Z = in excess of 240klm or 149 mph

In addition to the Z rated tyres the tyre manufacturers also added a few other z rated tyres as the following

W = 270km/h or 168 mph

Y = 300km/h or 186 mph

The is quite a few more little changes to the wheel number system like T preceding the width size which indicates a temporary or run flat type of tyre, but most wheels will just have the basic info as described above.

Tags: Tyres Wheels Markings Numbers Sidewall