Getting the right tire size for your vehicle is incredibly important for safe handling, proper fit, accurate speedometer calibration, and to meet the load requirements of that vehicle. Tire sizes may seem like a mysterious sequence of numbers and letters, but understanding how to read the tire size codes is key to making sure your tires perform well.
This guide will cover the meanings behind tire size markings, where to find your recommended sizes, and why properly sized tires matter when it comes to the safe operation as well as wear life of your vehicle’s tires. We’ll decode the sidewall lettering and numbering so you know just what your tire size specifications really mean.
What is Tire Size?
Tire size refers to the size measurements marked on the sidewall of your vehicle’s tires. It indicates the tire’s width, height, diameter, load index and speed rating. Getting the right tire size for your vehicle is important for proper fit, safety and performance.
Where to Find Your Tire Size?
Tire Sidewall – Your vehicle’s tire size is marked directly on the sidewall. Look for a series of numbers and letters, such as P215/55R17.
Vehicle Manual – Check your owner’s manual for recommendations on original equipment tire sizes for your make and model.
Tire Retailer Websites – Many online tire retailers have tire size lookup tools where you enter your vehicle year, make and model and it displays the recommended tire sizes.
How to Read Your Tire Size Correctly?
Your tire size will be a combination of numbers and letters, usually looking something like this: P215/65R15. I know, it looks like alphabet soup! But each set of numbers and letters tells you something specific about your tire.
First up are the letters “P”, “LT”, or “ST”. The “P” stands for passenger vehicle, “LT” stands for light truck (used for heavy loads) and ST stands for special trailers (used for trailers). This tells you what type of vehicle the tire is made for.
After that you’ll see three numbers, such as “215.” These numbers represent your tire’s width in millimeters. So in my example, 215 means the tire is 215mm wide – about 8.5 inches.
The next part is a forward slash followed by two more numbers, such as “/65.” This is your aspect ratio. That’s the relationship between the tire’s height and width. So a 65 aspect ratio means the tire’s sidewall height is 65% of the width.
After the aspect ratio you’ll probably see another letter, typically an “R.” The “R” stands for radial, which is the kind of construction used in most modern tires.
Finally, the last number represents the diameter of your wheel in inches. So “R15” means the tire fits a 15-inch wheel.
Is Getting the Correct Tire Size Important?
Getting the correct tire size is extremely important for the proper functioning of your vehicle, safety, and performance.
The tire size indicates the exact tire dimensions that are engineered to match the requirements and specifications of your particular vehicle make and model. Using the wrong tire size can negatively impact handling, braking distances, speedometer/odometer accuracy, wheel wells clearance, and even fuel economy.
For instance, a smaller tire will have less surface area in contact with the road. This reduces traction, making acceleration, braking, and turning more difficult and hazardous. Similarly, a larger tire may rub against mechanical parts or not fit properly in the wheel well. The extra weight of oversized tires also puts more strain on the engine, increasing fuel consumption.
Additionally, the wrong size tires throw off your vehicle’s geometry alignment. Vital systems like the anti-lock brakes and all-wheel drive depend on tires of the recommended dimensions to work effectively. Even subtle size differences can confuse the advanced sensors in these technologies.
With so many vital performance and safety aspects tied to tire sizing, it’s easy to see why using the manufacturer recommended specifications is crucial. The specialized engineering teams at automakers design each element like tires to operate in harmony. Just a little variance can undermine the carefully calibrated vehicle dynamics. Sticking to the proper sizing ensures optimized functionality.
So yes, correct tire sizing affects everything from ride quality and wheel alignment to safety features and operating costs. It’s absolutely essential to double check and get the right sized tires for your make and model.
The Other Tire Markings Meaning
In addition to the tire size marking, there are several other cryptic-looking codes and numbers imprinted on tire sidewalls. Let me demystify a few of the common ones for you:
Tire Load Index – This is a numerical code ranging from around 60 to over 120. It specifies the maximum load carrying capacity the tire is rated to handle. Higher numbers denote a greater weight capacity.
Treadwear Grade – This 3-digit number predicts the tire’s wear rate, with higher grades like 400 meaning slower tread wear and thus better mileage. It’s useful for comparing relative tread life between tire models.
Traction Grade – Represented by the letters AA, A, B, or C, this denotes a tire’s ability to stop on wet roads. AA is the highest rating, meaning shortest stopping distance.
Temperature Grade – Typically A, B, or C, this grade rates how well a tire dissipates heat while driving. The highest A grade can withstand greater sustained high-speed driving without overheating.
UTQG Code – Combining the treadwear, traction and temperature grades, this 3-part code provides an easy snapshot of a tire’s key performance parameters.
