How To Read A Tire Sidewall

February 15, 2010

All tires come with a code that tells you what they are and for what they should be used. This code is made up of several numbers and letters, each indicating a specific characteristic of the tire. When it comes time to research and buy new tires, these can be a bit overwhelming.

There are really just a few things you'll need to know when it comes to replacing your vehicle's tires. The nice thing is that duplicating the specs of the tires you already have is usually a safe bet. If you still want to know why they're right for your car, read on for a breakdown what the tire code means.

Let's use this sidewall code as an example: P225/65 R16 89S

Starting with the beginning, the first letter indicates the tire type.  In our example, the 'P' stands for passenger vehicle. Other service types you might encounter include 'LT' (light truck), 'T' (temporary), 'ST' (special trailer), and 'C' (commercial). The absence of a letter at the beginning indicates a European tire code that is effectively the same as a 'P' type.

Next is a number that indicates the width of the tire in millimeters. The sample tire here would be 225 millimeters wide. Higher numbers, of course, mean wider tires. This is pretty straightforward, but very important for the proper fit of your tires.

The width is followed by another number, '65' in this case. This is a ratio, or percentage, of the sidewall height compared to the tire width. The height of this tire's sidewall is 65% of its width. A lower ratio here indicates low profile tires, generally associated with higher performance. Tires with higher ratios are generally associated with a more comfortable ride.

After this, there is a letter that will tell you how the tire is constructed. Our sample tire is a radial tire. A 'B' indicates bias construction. The difference between the two types is the orientation of the layers that make up the tire.

Another important size you must understand is the rim diameter, which is shown directly after the 'R'. The example here must be mounted on a 16 inch rim.

After all of that you'll see one more number/letter combo. The number in this combo is the load index. It will fall on a scale from 60 to 125, matching up with a weight capacity of 551 to 3,638 lb.

Finally we have the speed rating. This will tell you the tire's maximum recommended operating speed. Here's a breakdown of the speed codes:

L: 75 mph
M: 81 mph
N: 87 mph
P: 93 mph
Q: 99 mph
R: 106 mph
T: 118 mph
U: 124 mph
H: 130 mph
V: 149 mph
W: 168 mph
Y: 186 mph

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