Installing the correct tires on your vehicle is important for overall performance and safety. Your choice of tire should reflect your driving conditions and preferences including longevity, response and handling. Understanding the size tire your vehicle requires is the first step to buying the right tires.
It’s also important to know when to replace your tires.
WHERE CAN I FIND MY TIRE SIZE?
You can find your vehicle’s tire size in the owner’s manual or on the vehicle placard located on the driver-side door frame. If you know your tires are the original equipment (OE) tires that came with your vehicle, then you can check the tire sidewall for its size. Regardless where you find it, you will need to know how to read tire sizes first.
Besides size, other factors such as load index and speed rating should also be considered when tire shopping. Getting a general idea of the construction of a tire will be helpful.
Treadwell is a great way to find the right sized tires for your vehicle. Simply input your vehicle make and model, where and how you drive, and it will give you the best tire matches possible. It’s what our techs use in store to help you find the best tires for you.
HOW TO READ YOUR TIRE SIZE
Let’s use a sample tire size to explain the meaning of each measure found in your tire’s size. One of the most common tire sizes is P205/55R16 91H.
Tire Type
Many tires include a letter indicating their tire type. In our example, “P” stands for “P-metric,” meaning it is a passenger tire.
Other tire types you might see include:
P: P-type tires are designed for cars, crossovers, and light duty pickups.
LT: Light truck tires; designed for ¾ and 1-ton pickup trucks, SUVs, and full-size vans
T: temporary spare tires; should only be used in an emergency
Sometimes you will notice there is no letter code. This usually means it is a “metric” tire that originates in Europe. These have the same dimensions as P-metric but were developed using globally recognized European standards. We go into depth about Euro-metric and P-metric tires here.
Tire Width (Section Width)
Following the tire type, you will see a three digit number representing the tire’s width (or section width). This is measured in millimeters and refers to the distance between the furthest points of the tire’s two sidewalls.
A large width indicates a wider tire. Our example tire has a width of 205mm.
Aspect Ratio
Following the tire’s width is a slash and a two digit number. This is the aspect ratio, which gives the tire’s height.
Specifically, aspect ratio is the tire’s sidewall height as a percentage of the width. A high aspect ratio means that a tire has a larger sidewall while a lower ratio means a lower sidewall.
Our sample tire size has an aspect ratio of 55, meaning the tire’s sidewall height is 55% of the width.
Tire Construction
After the aspect ratio, you’ll find a letter that signifies the tire’s construction type. There are two types:
R: Radial tires are composed of plies that run perpendicular to the bead and the ground. Passenger tires are commonly radial construction.
D: Bias tires are made from plies that crisscross in layers. Bias tires tend to be found on heavy-duty equipment, machinery, and off-road tires because they have high load capacity and extreme durability. They are also common on classic and vintage vehicles.
Rim Diameter
After the construction type is the rim diameter. This refers to the size of the wheel the tire fits on and is measured in inches. Common wheel sizes range from 14 to 17 inches but larger ones are increasingly popular.
Our example wheel has a rim diameter of 16 so it can only be mounted on a 16-inch wheel.
Load Index
You’ll find the load index after the rim diameter. The load index indicates the maximum load-carrying capacity of a tire. This value has a corresponding load measured in pounds and can be found on a standardized laid index table.
Our example tire size has a load index of 91, meaning it can support 1356 pounds at maximum inflation (as per the load index table).
It’s important to make sure your tires are properly inflated for maximum performance and safety. We teach you how to check your tire pressure here:
Speed Rating
Finally, the tire's size ends with a single letter to represent its speed rating. This indicates a tire’s maximum speed capability as determined by laboratory testing.
Our sample tire has a speed rating of “H” which means it has been tested to safely reach and sustain speeds of up to 130mph.
Speed ratings vary according to the tire’s purpose. For example, family commuting vehicles such as sedans and vans are typically T-rated (up to 118mph) but ultra-high performance vehicle tires can have V-rated (up to 149mph) and exotic sports cars can have W or Y-rated tires (up to 168-186mph).
If you need exact tire measurements, check out our tire size calculator for precise measurements using your tire size.
Ready to roll?
If you have any questions or are unsure what tires work best for you, drop in or give us a ring. We’ll get you taken care of. Buy and book online and save time in-store!