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How to Read Tire Size

When it comes time to replace your vehicle’s tires, you may find yourself with questions like, “What size tires do I need?” Fletcher Jones Motorcars of Fremont is here to help you understand how to find the right tire size, so you can make sure you get the right Mercedes-Benz Original Tires for your vehicle. 

What Do Tire Sizes Mean?

Tire SizeThe size indicated on the sidewall of your tires indicates the type of vehicle the tire can support. From wheel size to maximum pounds it can carry, it’s important to understand how to read tires sizes to ensure you’re picking the tire your vehicle needs to function. If you need help choosing the right Mercedes-Benz approved tire for your luxury vehicle, reach out to the Fletcher Jones Motorcars of Fremont tire center

How to Tell Tire Sizes: What the Markings Mean

What can seem like a random string of letters and numbers is actually a sequence of codes that share information about your tire’s size, construction, and more. Take a closer look at the sidewall of your tire, and then compare what you see with the breakdown below: 

Tire Type

Tire class is the first thing indicated on the tire. Passenger vehicles are marked by a “P,” light trucks are coded with an “LT,” and Euro metric tires are absent of any lettering. 

Tire Width

Next comes a three-digit number which denotes the tire’s width. The tire width measurement is done in millimeters and is measured from one sidewall to another. So, if you have a tire that’s marked with “P245/,”  you’re looking at a passenger tire class tire with a measurement of 245 millimeters. 

Aspect Ratio

Next comes the aspect ratio, which is the ratio of the height of the tire’s cross-section to its width. This will be represented by a two-digit number.  


The next letter communicates the construction of the tire. Built using layers of fabric, the most common type of tire is a radial tire. Noted by the letter “R,” these tires have cords that run at right angles to the circumference of the tire. Using this construction method reinforces the tire allowing for improved performance. 

Wheel Diameter

Need to make sure your tire fits your wheel? The wheel diameter shows the measurement in inches of the wheel a tire will fit. A number “18” means your tire will fit an 18-inch wheel. 

Load Index

The maximum load a tire can carry while properly inflated is called the load index. On a tire, this number is found after the wheel diameter. To make sure your tire can meet the demands of your vehicle, you’ll need a tire with a load index that meets or exceeds the specifications set by your vehicle’s manufacturer.

Speed Rating

The next letter is the speed rating of your tire, which is separate from the speed capabilities of your vehicle. With a top speed of 99 mph, the speed ratings of tires start with “Q” tires. Ratings continue up to “(Y)” which are for tires built for speeds above 186 mph. Whatever the speed rating for your tires may be, though, posted speed limit signs and road conditions still need to take precedence. 

Other Tire Codes & Markings

After these markings come additional symbols, some of which are optional and some of which are not. Other symbols you may see on your tire include: 

DOT Symbol

The Department of Transportation has minimum standards for all tires to be sold in the U.S. To indicate your tire has passed required testing, it will be marked with “DOT.” After this, you’ll find another letter and number which point to the plant the tire was manufactured at. Tire size is also indicated here by two more letters. 

Tire Identification Number

After the required “DOT” symbol, there may be some optional markings. These will be a series of letters and numbers and may be included by the manufacturer to share information about the tire tread, construction, and the week and year the tire was fabricated. 


UTQG, or Uniform Tire Quality Grading, is a rating system that grades tires based on tread wear, traction, and temperature resistance. Developed by the U.S. Department of Transportation, ratings run from A to C for traction and AA to C for temperature, C being the lowest ranking on the UTQG scale. Testing for this is done by manufacturers and doesn’t dictate the lifespan of the tire but instead focuses on durability. 

Maximum Tire Pressure & Load

The letters “PSI” preceded by a number note the maximum amount of tire pressure the tire can hold and operate with. Noted by a number followed by “LBS,” this is the maximum load in pounds that a tire can carry when the tires are at maximum inflation. Keep in mind, these are not the numbers recommended for ideal vehicle performance. Check your owner’s manual for actual recommendations for optimal performance. 

What Size Tires Do I Need for My Vehicle?

So, now you can answer the question, “What do tire sizes mean?” but that doesn’t tell you what tire sizes you need for your vehicle. You can find this information in your owner’s manual, or our technicians can help pair your vehicle with the tires you need for the best performance and fit. 

Get Mercedes-Benz Tires Near Hayward

Union City and Dublin drivers in need of tire maintenance, repairs, or replacements can find what they’re looking for at Fletcher Jones Motorcars of Fremont. Get started by contacting us or shopping our tires online today! 


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