How to Read Tire Size

how to ready 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 Stratham, Portsmouth, and Exeter, NH, and beyond, we’ve created this brief step-by-step guide so you know exactly what those letters and numbers mean. Contact us with any questions!

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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 2-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.

Construction

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 2-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 the tire 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.

How Often Will You Need New Tires?

Now that you know how to read tire size, you should be able to tell different tires apart. So, how often will you need to look at tire size anyway? That depends on how often you need to buy tires. While lots of vehicle maintenance is done pretty regularly, replacing your tires is a little different.

That’s because it’s tough to tell how often you’ll need new tires. You could go years without getting a flat tire or you could drive over a nail tomorrow. When it comes to how long your tires last, that really depends on how you drive.

For example, an aggressive driver is going to need to replace their tires more often than someone who obeys the speed limit, takes smooth roads, and comes to a gradual stop. Since things like terrain and driver habits can impact your tires, tires can last anywhere from 35,000 to 75,000 miles.

That means your tires could last for years. However, even if your tires still look good as new, you should never go more than 10 years without replacing them.

Replace vs. Rotate Your Tires

Chances are you’ve heard the term rotate your tires. What’s the difference between rotating and replacing them? Essentially, rotating your tires means moving them from one axle to another. This is to help them wear down evenly and last longer. It’s an important part of your routine maintenance.

Whenever you bring your BMW in for service or an inspection, our service technicians will inspect the tires to see if they should be rotated or replaced. Once the tread gets too worn, they won’t bother rotating them again. They’ll recommend a new set of tires for you.

How to Tell if You Need New Tires

There are a few ways to tell if it’s time to look for new tires. The most obvious one is if you walk into your garage one morning and see that you’ve got a flat tire. Aside from that, there are a few warning signs you can look for, including:

Tire Pressure Monitoring Light

Bulging or Tearing Sidewalls

Worn Down Tread

Tire tread wears over time. One way you can tell that it’s severely worn is by seeing if your tires have started to look smooth or shiny. Another way is to run your hand over it. If it feels slightly smooth but you’re still not sure, there’s a quick test you can do.

The penny test is a timeless way to see how deep your tread is. Just take a penny, turn it upside down, and stick it in the grooves of your tire tread. If you can see President Lincoln’s head, your tread has gotten to the point where it’s time to look for new tires.

Schedule Tire Service with BMW of Stratham!

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, New Hampshire, areas, don’t hesitate to call or stop by BMW of Stratham with any questions you might have about how to read tire size.

Whether you need new tires, have a flat, or believe it's time to get your tires rotated, our service center is here to help. With our team of ASE-certified technicians, your vehicle will be in good hands. They’ll help you choose the best set of wheels for your BMW and get you back on the road in little time. Contact us to learn more or schedule tire service online anytime.

Our Reviews

DealerRater Jan 20, 2025

Matt in service was excellent to interact with. Thank you for all the aasistance - much appreciated.

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