What do tire sizes mean? In short, tire sizes are a way for owners to know they’re picking a tire that works with their vehicle. If you’re not sure how to read tire sizes, no worries! Mercedes-Benz of Ontario has put together a guide on how to find tire sizes and what they mean! Before choosing a replacement tire for your vehicle, reference our guide below.
Your tire’s sidewall will be marked with a string of letters and numbers that represent different aspects of your tire construction and size. To better understand these markings and their meanings, review the following information:
The first letter on your tire is the indicator of the tire class. The letter “P” denotes the tire is for a passenger vehicle, while an “LT” means the tire is designed for light trucks. If you don’t see a letter, you’re looking at a Euro metric tire.
Following the tire class is a three-digit number. This number is the tire width, and it’s the measurement in millimeters from one of the tire’s sidewalls to another. For example, if you see “P245/” on your tire, that means you have a passenger vehicle with a tire width of 245 millimeters.
After the tire width and slash mark comes a two-digit number called the aspect ratio. Aspect ratio refers to the height of the tire’s cross-section to its width.
Behind the aspect ratio, you’ll find a letter that describes the construction of the tire. The letter “R” is the most common marking and indicates a radial tire. Radial tires are built with layers of fabric with cords that run at right angles to the circumference of the tire. Drivers can expect increased performance from these reinforced tire treads.
The next two-digit number is the wheel diameter and specifies the measurement in inches of the wheel a tire will fit. So, if you see the number “19,” this means your tire will fit a 19-inch wheel.
The load index number, found after the wheel diameter, references the maximum load a tire can carry while properly inflated. When choosing a tire, review the specifications set by your vehicle’s manufacturer, and choose a tire that meets or exceeds those needs.
Speed rating comes in the form of letters found after the load index. Normally, tires start with the “Q” rating, which means that the tires are able to handle a top speed of 99 mph. Speed ratings end with “(Y),” which denotes tires built for speeds above 186 mph. Regardless of your tire’s speed rating, it’s worth noting that weather, road conditions, and, of course, posted speed limit signs all need to be taken into account when operating your vehicle.
In addition to the tire size and construction markings listed above, you’ll find other tire codes and markings on your tires. These can include:
The Department of Transportation marking, displayed as “DOT,” is required to show that the tire has passed all the minimum DOT standards to be sold in the U.S. Another letter and number follow and share where the tire was manufactured at. Past that, there are two more letters that indicate the size.
Next up you may find an optional code consisting of a series of letters and numbers. This may have been placed by the tire’s manufacturer to indicate tire tread, construction, and the week and year the tire was created.
Uniform Tire Quality Grading (also known as UTQG) is a system that has been developed to rate tires based on tread wear, traction, and temperature resistance. Created by the U.S. Department of Transportation, this tire rating system awards ratings which run from A to C for traction and AA to C for temperature. With this scale, C indicates the lower ranking.
Maximum tire pressure is the most air pressure a tire can hold and operate with. This is marked by a number followed by the letters “PSI”. The maximum load references the amount in pounds that a tire can carry when the tires are at maximum inflation. This is marked by a number followed by the letters “LBS.” These are absolute maximums, not the numbers recommended for ideal performance. To see what specs are optimal for your vehicle’s performance, we recommend checking the owner’s manual.
Now that you know how to read tire sizes, you’re halfway there. Still, you need to be able to answer the question, “What size tires do I need,” to make the right purchase. You can start by checking your owner’s manual or by following up with the Mercedes-Benz of Ontario tire center. Our techs will help you find the Mercedes-Benz Original Tire for your vehicle and performance needs.
If you’re in the Fontana or Chino area and looking for new Mercedes-Benz tires or help with Mercedes-Benz tire maintenance, schedule a consultation with our tire center. We can make recommendations for repairs or set you up with a new set of well-fitting tires today!
