Know Your Tires: How to Read Your Truck Tire Size

Tires don’t last forever, so you will replace them eventually. A tire’s average lifespan is six years, and using your tires beyond that window can be risky. Car experts assert that tires older than the specified timeframe are less durable and compromise driver safety.

Once it’s time for your car to get a tire replacement, you should take the time to read your tire size and specs. Read on to learn how to read your tire size plus other useful information about tire replacement and maintenance.


How to Read Your Tire Size

Your tire’s sidewall contains different types of information. You may find some variations in tires from various manufacturers, but all tires typically follow the same format.


1. Tire class or vehicle type

Most tires indicate a “service description.” A tire service description is a standardized number marked into the tire right next to its size. Compared to passenger vehicle tires, truck tires usually have more numbers to indicate more details.

The naming also varies for truck tires and passenger vehicle tires. For truck tires, the R22.5 part of the service description is usually the rim size of the truck.

While it’s not always present in some tires, it’s an essential information you should know since it also indicates your automobile’s tire class and vehicle type, along with other important information.
In terms of tire designation, the following letters correspond to a specific vehicle type:

  • P – Passenger
  • LT – Light Truck

Finding a letter “P” before the numbers indicate tire sizing is based on the “U.S. metric.” Otherwise, they are sized according to the “Euro-metric.” Tire-sizing in the Philippines uses the U.S. metric.


2. Section width

The first number on your tire description is your tire’s section width, typically measured in millimeters. Tire width states the measurement from one sidewall edge to another. For instance, if you have a tire that has a marking of P175, the tire is for a passenger car, with a nominal width of 175.

Generally, trucks tend to use higher figures. In that case, the tire description equates to a wider tire.


3. Aspect ratio

Aspect ratio refers to the sidewall’s height and is found in the tire description after the slash marking. The vehicle aspect ratio is calculated in percentages, dividing the tire height off the rim by the section width. If your tire has an aspect ratio of 60, its tire height is 60% of its width.


4. Tire construction

Next to the aspect ratio is the tire construction. Commonly identified by the letter “R” in the tire description, tire construction refers to the tire area that encounters the road and provides tread wear and traction. The letter R stands for “radial tires,” which are considered the industry standard for passenger car tires.

Radial tires’ internal ply cords are positioned in a radial direction, perpendicular to the rotation direction.

In some cases, you may also find the letter “D,” which means “diagonal bias-ply tire.” Alternatively known as “old-fashioned” bias-ply tires, diagonal tires are commonly used on trucks and trailers.

For Triangle Tires, you may sometimes see a “C” after the wheel diameter, as in 185R14C. This means that the tire is made out of 8 ply and is fit for commercial use.


5. Wheel diameter

Based on the service description sequence, the wheel diameter appears following the tire construction. The wheel diameter is measured in inches. It is the distance measured across the wheel’s face, from one bead seat to the next.

Suppose you have a wheel with a P215/65R15 tire service description. In that case, you should purchase a rim with a 15-inch diameter.


6. Load range/ply rating

One of the essential details in a tire service description is its load range or ply rating. Typically found next to the wheel diameter, load range indicates how much weight your tire can accommodate when fully inflated.

Before replacing your tires, it’s best to refer to the load-carrying capacity per tire chart to get the correct tire size for your vehicle. Load range may vary depending on the metric used. Tires sized using the P metric will have a ply rating one or two points lower than Euro metric tires.


7. Speed rating

The last figure in the tire service description is the speed rating. In contrast with the ply rating that corresponds to a specific load, the speed rating is marked with a letter stating a particular speed capability.

Suppose you have a tire that has an “R” marking. Based on the speeding chart, a tire with an “R” rating can withstand a speed of 106 miles per hour. Depending on the speed rating letter, different tires can accommodate varying speeds. Here is what each letter in a tire’s speed rating means:

Speed Symbol Speed (km/h) Speed (mph)
A1-A8 under 40 under 25
B 50 31
C 60 37
D 65 40
E 70 43
F 80 50
G 90 56
J 100 62
K 110 68
L 120 75
M 130 81
N 140 87
P 150 94
Q 160 99
R 170 106
S 180 112
T 190 118
U 200 124
H 210 130
V 240 149
Z over 240 over 149


Greasing the Wheels

Tire size plays a significant role in vehicle performance. Regardless of the kind of vehicle, the right tire size can improve its durability and promote driver safety.

As such, you must know how to read your tire size. While some people unintentionally neglect to learn how to read a tire, having this information handy can make driving easier.

If you’re looking for quality replacement tires, Triangle Tires can help. From passenger cars and light trucks to heavy equipment vehicles, we offer a wide array of tires for delivery at an affordable price. Browse our tire catalog or contact us for inquiries.

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