How to Read Tire Size

tire size

Have you noticed the combination of letters and numbers embossed on the sides of your tires? Have you ever wondered what they meant? Apart from tire size, this writing contains other important information about your tires. At BMW of Stratham, we think it’s a good idea for all drivers to know as much as possible about their cars. After all, you never know when that information might come in handy.

For those of you who live in the Stratham, Portsmouth and Exeter area, we’ve created this brief step-by-step guide so you know exactly what those letters and numbers mean. Contact us with any questions!

Type of Tire

Take a moment to look at your tire. The first letter there is most likely a P. This indicates the type of tire that you have. The P means you have a P-Metric tire. A P-Metric tire is one that was made in the U.S. in accordance with strict passenger vehicle guidelines. If you have a light truck, your tire will have an LT. This can be found at the start or at the end of the tire size. If there is no letter at the beginning, you have a Euro-Metric tire that may have different load capacities.

Width of Tire

The three digits that follow the P in the tire size tell you the width of the tire from sidewall to sidewall and is shown in millimeters.

Aspect Ratio

Next, you’ll see a slash mark. The two-digit number that comes after the slash mark is the aspect ratio. This tells you the height of the tire sidewall. It is a percentage of the tire’s width. For example, if your tire size starts out as P205/55, your tire’s height is 55% of its width.


The next part of the tire size describes its construction. The letter R stands for radial. Most contemporary tires are radial tires.

Wheel Diameter

The two-digit number that comes after the R tells you the diameter of the wheel that your tire matches.

Load Index Number

Next is the Index load number. This indicates your tire’s maximum load capacity.

Speed Rating

The speed rating is the last aspect of tire size. It tells you the maximum speed the tire is capable of reaching.

Other Markings

Besides the tire size, other markings on your tires are good to know. They are as follows:

  • DOT Symbol. When you see this on your tire, it means it meets the Federal Motor Vehicle Safety Standards.
  • Tire ID Number. This number tells you where and when the tire was manufactured.
  • Air Pressure. The maximum pressure number tells you how much air pressure your tire can hold.

Stop By Anytime

Now that you know what all those markings on the sides of your tires mean, you can find any of the above information whenever you need it.

If you live in the Stratham, Portsmouth and Exeter areas, don’t hesitate to call or stop by BMW of Stratham with any questions you might have about how to read tire size.