How to Read Tire Sizing

Tire Size Diagram

Vehicle Type (P):

This letter indicates the type of vehicle. “P” stands for passenger car. There are two different metrics for vehicle type. The P-metric and the Euro-metric. The P-metric is for vehicles made to carry passengers, hence, “passenger car.” This includes cars, SUVs, or light-duty pickup trucks. The Euro-metric is not much different. In simple terms, Euro-metric tires are made to withstand a higher load capacity. Generally, one can use Euro-Metric tires on P-metric tires, but not vice versa, since P-metric tires withstand a lower load capacity. It is recommended, however, to use the same tire metric that came with your vehicle. Euro-metric tires have the same format as P-metric, but do not include the “P.” You might also see “LT,” which stands for Light Truck.

Width (225):

The first number on the tire is the width in millimetres, from sidewall to sidewall. This specific tire has a width of 225 millimetres.

 Aspect Ratio (70):

This is the tire’s aspect ratio, which is the height of the tire’s sidewall expressed as a percentage of the width. The tire’s sidewall is 70% of 225, roughly 157.5 millimetres in this example.

 Tire Construction (R):

This stands for radial tires, the most common type of tire found today. Radial indicates the direction of the tire’s ply-chords. The ply cords in a radial tire are arranged perpendicular to the direction of travel. The other type of construction is “B” or “D” for Diagonal of Bias Ply. Occasionally, you might see a “Z” before the “R,” which refers to the highest speed rating (see speed rating chart in the speed rating section)

 Wheel Diameter (16):

This number indicates the wheel size (in diameter) that fits the tire at hand. In this example, this tire fits a 16-inch wheel.

 Load Index (91):

This is the load index of the tire. A 91-load index means that one tire can hold roughly 1,356 pounds. A set of four tires can carry 5,424 pounds.

There are two load types that you might see on a tire. Standard Load and Extra Load, where the only difference is an “XL” at the end of the tire size. For example, P225/70R16 91S XL.

Another aspect to look at is the difference between P-metric and Euro-metric compared to LT-metric and Euro-metric commercial. The former will only have one load index number, whereas the latter will have two, separated by a slash. The first number is when the tire is used in a single application, and the second for dual application.

Tire Load Index Chart

Speed Rating (S):  

This is the speed rating. An “S” rating means the tires can support a speed up to 180km/h. Passenger vehicles are typically on the lower end, ranging up to higher ratings for performance vehicles. If your vehicle is equipped with tires of different speed ratings, then the vehicle’s top speed is determined by the tire with the slowest speed rating.

Tire Speed Rating Chart

Where to Find Your Tire Size 

• The first place you can find your vehicle’s tire size is on the sidewall of your current tires. When replacing your tires, you typically want to find ones that match your current tires.
• The owner’s manual in the glovebox compartment is the second place to find tire sizing.
• Thirdly, the gas tank hatch also holds information about tire sizing.
• Lastly, the driver’s side door also holds tire sizing and specification information.

Uniform Tire Quality Grading

Another informative aspect found on tires is the Uniform Tire Quality Grading or UTQG, which is included on P-metric and Euro-metric tires. The rating, however, is only required for all-season and summer tires. To help buyers make effective decisions, UTQG consists of three aspects: Treadwear, Traction, and Temperature.

UTQG Ratings

Treadwear

The treadwear imprint demonstrates the lifespan of a tire. Treadwear ranges from levels of 100 to 1000. As an example, a tire with a treadwear rating of 600 lasts twice as long as that with a 300 rating. The rating is determined through a 7,200-mile test, driven in 400-mile increments in Texas developed by the National Highway Traffic Safety Administration (NHTSA).

Treadwear Rating	Mileage (Not Exact)
100-200	32,100 Kilometers
201-300	32,100 - 48,200 Kilometers
301-400	48,200 - 64,300 Kilometers
401-500	64,300 - 80,400 Kilometers
501-600	80,400 - 96,500 Kilometers
601-700	96,500 - 112,600 Kilometers
700-1,000	128700+ Kilometers

Traction

The traction grading demonstrates a tire’s performance during wet conditions. There are four traction gradings. AA, A, B, or C, AA being the highest and C the lowest.

Temperature

Temperature ratings demonstrate the tires’ performance during high-speed or warm weather, where the tires build up high amounts of temperatures. Tires with lower temperature ratings can blow when they get too hot. The temperature ratings are A, B, and C, where A is the highest, and C is the lowest.

Temperature Rating	Speed
A	185 and above
B	160-185
C	136-160