The tires on your vehicle are required to support the weight of your vehicle, absorb shock on roads, provide traction, and maintain direction or help with changes in directions. While your vehicle can start and run without tires, it won’t get far without them. That said, tires have a lot of information on the sidewall and other parts of the tire. You might be content with knowing that you have tires but it’s important to understand every element of a tire. In doing so, you’ll be able to make better choices and get tires that work the best for your vehicle.
The writing on the side of a tire is the tire’s code and specs. Tire codes are made up of a combination of letters and numbers and the codes that tire manufacturers use are universal, so you don’t have to worry about knowing different information for different brands. In our guide, we’re going to take you through the types of tires, the codes on tires, and what it all means.
We’ll be focusing on the basic types of tires, which are rated based on the surface it’s designed for (road or off-road), the type of vehicle the tire goes on, and the components that go into making a reliable automotive tire.
Read on to learn everything you need to know about tires.
What Is a Tire?
A tire is a circular component that covers a vehicle’s rim, which is a metal circle that’s fastened to the car with lug nuts. Automotive tires are pneumatically inflated and provide a vehicle with the means to drive on surfaces. Tires accomplish this by providing a flexible cushion that manages and absorbs shock as tires roll over surfaces. Tires give vehicles a contact patch, which matches the weight of the vehicle with the strength of the surface it’s riding over. The primary reason for different tire types is because of this contact patch.
What Are Tires Made Out Of?
Automotive tires are pneumatic tires made out of a combination of rubber, synthetic rubber, and carbon black. Some tires also include tread compounds like silica treads, which provide greater rolling resistance. Tires are also filled with air, which inflates the tire.
While most tires are pneumatic, there are exceptions. For example, forklifts and other heavy equipment use solid (non-pneumatic) tires because of the load demands.
Parts of the Tire
Tires appear basic but many parts make up the whole tire you see on your vehicle. These parts vary based on the tire but the common ones include:
- Treads: The tread of a tire is the part of the tire that touches the road and forms a contact patch.
- Beads: The tire bead is what connects the tire to the rim, which is commonly done with steel wire.
- Sidewall: The sidewall is a thick part of the tire that separates the tread from the bead.
- Shoulder: The shoulder is the edge of the tread that transitions to the sidewall
- Piles: Piles are cords embedded in the rubber that helps the tire hold its shape.
In most cases, these parts of the tire contribute to its performance and specifications.
Components of a Tire
Tires on vehicles have several components you should be aware of. These components are the valve stem and the tubing on the inside of a tire. The valve stem is a small stem that sticks out from the tire. The valve stem is how compressed air is delivered to the tire. The inner tubing is found inside the tire and is made out of a torus-shaped, rubber, or synthetic rubber balloon. Inner tubes are then inflated and designed to prevent air from leaking out of the tire.
While there are specific components found on other tires, these are the primary components you’ll find on your average passenger vehicle.
Tire Designs
Tires are made from many different materials but the general designs of tires have changed over the years. There are several types of tire designs but the most common are radial tires, bias tires, and belted bias tires. Today, most tires on the road are radial tires.
Radial Tires
Radial tires are designed with body ply cords that extend from the beads and across the tire’s tread. For radial tires, cords are laid at right angles to the centerline of the tire’s tread and parallel to each other. The tires are then fitted with stabilizing belts beneath the treads, which are typically made from durable cord or lightweight steel.
Bias Tires
Bias tires (cross-ply tires) use body ply cords at 30-degree and 40-degree angles. They’re laid at opposing angles which forms a crisscross pattern. These tires are more flexible than radial tires but that comes with less durability.
Belted Bias Tires
Belted bias tires have two or more bias piles. The stabilizer belts are bonded beneath the tire’s tread. These tires were made popular by Goodyear but don’t see extensive use today.
While these are the most common tire designs, there are others but they’re used for industrial equipment and special equipment.
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Types of Tires Based on Vehicle
To begin, it’s important to consider the types of tires based on the vehicles they’re meant for. This is one of the easiest methods to know what tires you need and how they work. There are four types of tires, each one for a different type of vehicle. The types of tires are:
- (P): Passenger
- (LT) Light truck (think pickups and vans)
- (ST): Special trailer
- (T): Temporary
While these tire types specify which vehicle they’re supposed to go on, tires can be used on different vehicles in special situations. For example, an off-road tire designed for a light truck can work well on an off-road rally car like a Subaru WRX.
Passenger Tires
Passenger tires are designed to pass Tire and Rim Association (TRA) guidelines. TRA guidelines are reviewed annually and ensure that manufacturers comply with tire standards. This includes testing, operation, and the materials used in manufacturing. Passenger tires have a (P) symbol and begin the tire code on the side of the tire. If a tire doesn’t have a letter in front of the code, the tire is not in compliance with TRA guidelines. In these cases, tires are typically following ETRTO standards instead.
Passenger tires are commonly found on vehicles like:
- Coups (two-door sports cars)
- Sedans
- Crossovers
Passenger tires shouldn’t be used on other vehicle types.
Light Truck Tires
Light truck tires will have an (LT) symbol in front of the tire code. Light truck tires are designed to be more durable and aggressive than passenger tires because light trucks are heavier and more demanding.
You’ll find light truck tires on:
- Vans
- SUVs
- Pickup trucks
- Off-road vehicles
While light truck tires are made for larger vehicles, they can also be used on passenger cars with off-road modifications. We don’t recommend using them otherwise because the ride quality can decrease.
Special Trailer Tires
Special trailer tires will have an (ST) symbol to begin the tire code. Special trailer tires are unique tires used for trailers and equipment that requires towing. These tires are durable but don’t have great ride quality. That said, ride quality isn’t important for special trailer tires because people aren’t typically riding in trailers.
You’ll find special trailer tires on vehicles like:
- Trailers
- Horse carriers
- Boat trailers
- Special construction equipment
Special trailer tires should only be used on trailers because of the poor ride quality.
Temporary Tires
Temporary tires have (TT) as the first letter in the tire code. These tires are also known as donuts because of their small size and lack of visual appeal. These tires are legal to drive with but they have special speed requirements (like driving under 55) and should only be used temporarily.
You’ll find temporary tires on:
- Agricultural equipment
- Cars using a spare
Temporary tires are not meant to be a permanent solution and should be replaced as soon as possible.
In most cases, knowing the type of tire you have is all you need to know before making a purchase. That said, you can narrow down your options by getting into the more specific aspects of a tire.
Tire Types Based on Surface
The four tire types are general guidelines for tires. Tires are categorized further by the surface they’re designed for and how they interact with road hazards like water, snow, mud, and ice.
There are several types of tires but the most common are:
- (A/S): All-season
- (T): Touring
- (P): Performance
- (A/T): All-terrain
- (M+S): Mud and snow
- (MT): Mud-terrain
While there are variations and subgroups, these are the common tire types based on the surface they drive on.
All-Season
All-season tires are designed for use in any season. These tires can handle snow, water, ice, and other hazardous conditions present within each of the seasons. While these tires can perform well during each season, they don’t excel at anything specific. Therefore, all-season tires are Jack’s of all trades but masters of none.
Still, all-season tires are the most common tires you’ll find. Most automotive manufacturers use these tires as OEM for their vehicles. They typically have a symmetrical tread pattern with thick grooves and sipes to evacuate water, snow, mud, and ice.
Touring
Touring tires are a hybrid between all-season tires and performance tires. These tires give drivers comfort on the road but aren’t great at handling hazardous conditions. Touring tires are also good for performance but not as good as performance tires. These tires also don’t last as long as all-season tires.
Performance
Performance tires are designed for on-road traction in warm conditions. These tires sacrifice comfort and ride quality for performance, which is why these tires are typically found on sports cars. They’re great for hugging the road, cornering, and racing.
Performance tires can be broken down into several subcategories:
- Summer
- Winter
- Competition
- All-Season
Summer
Summer tires are designed with performance and speed in mind. These tires perform well in dry conditions with tread designs that favor dry pavement. While they can handle wet conditions, they’re not as reliable as all-season tires in the rain or snow.
Winter
Winter tires are made for the winter. These tires have deep grooves and sipes to clear water from the tread. That said, the design limits the tire’s performance on dry pavement because of the rolling resistance.
Competition
Competition tires, or track tires, are made for racing. These tires don’t perform well on roads or wet conditions but excel on the pavement. Competition Tires can be found on vehicles that race around tracks.
All-Season
All-season performance tires have a shorter tread life than traditional all-season tires but perform better in the rain or snow. These tires can provide better braking and handling in wet and snowy conditions.
All-Terrain
All-terrain tires are designed for mild off-road use. They sacrifice some comfort for off-road performance and perform well on the road and off the road. These tires are great for people who like to go off-roading sometimes but also have to commute to work on highways and side roads.
Mud and Snow
Mud and snow tires are all-terrain tires that have more aggressive treads. These tires are great for handling mud, snow, and even ice. For these reasons, mud and snow tires can be found on any vehicle type and they work well for people who live in regions with cold winters.
Mud-Terrain
Mud-terrain tires are similar to all-terrain tires. The difference is that these tires have tread that wraps around the whole tire, which makes it easy to get rid of mud and rocks. The drawback to the design is that they will experience premature wear if driven on roads.
Competition Tires
Competition tires are unique tires used in off-road competitions. These tires have the most aggressive tread designs and work well off-road, in the snow, and in the mud. That said, they’re mostly useless on the road and very expensive.
How to Read Your Tire
There’s a lot of information on the side of your tires. While we’ve given you pieces of the puzzle, the entire tire code can be put together to give you an exact description of your tire. If you’re not familiar with tire codes, we recommend taking a look at the chart below.
That said, it’s important to break down each aspect of the tire code and what it means. While we’ve gone through a couple, there are other parts of the tire we haven’t gotten to yet.
Service Description
The service description is the first letter in a tire’s code. As mentioned above, the service descriptions are:
P: Passenger
LT: Light truck
ST: Service trailer
T: Temporary
Based on your vehicle’s load requirements, you’ll find these letters on your tire. Most vehicles will have a (P) or an (LT).
Tire Width
The width of a tire is the next part of the tire code. The tire width consists of a measurement in millimeters of the distance of the sidewall to the sidewall edge. The higher the number, the wider the tire.
Aspect Ratio
The aspect ratio is the next number in the sequence on the side of your tire. The aspect ratio is the section height compared to the section width. Lower aspect ratios are designed for handling, while higher numbers provide better comfort. An example number, 55, would be an aspect ratio of 55%. This would be good for cornering and handling.
Internal Construction
There used to be a handful of ways that manufacturers produced tires. While this used to be the case, most vehicles use radial tires. The “R” on the side of a tire means that it’s a radial tire. That said, some trucks might use bias-ply tires, which are represented by the letter B.
Rim Diameter
After the internal construction letter, you’ll find the rim diameter, which is measured in inches. If your vehicle has a 17 written on it, that means the rim’s diameter is 17 inches.
Load Index
The next number on a tire is the load index. The load index is indicative of how much weight a tire can hold. You have to use tire charts to determine the weight. For example, if you see “95” written on the tire that means it can carry a load of 1,521 pounds. You need to multiply that number by the number of tires on your vehicle to get the total load capacity.
Speed Rating
The last letter on the tire is the speed rating. The speed rating determines how fast a tire can reliably travel. There are several speed ratings, so we have the letter and corresponding speeds listed below:
S: 112 mph
T: 118 mph
U: 124 mph
H: 130 mph
Z: 149+ mph
W: 168 mph
Y: 186 mph
(Y): 186+ mph
Depending on how fast you’re going and the type of vehicle you have, making sure you have the appropriate speed rating is essential for your safety.
Traction Rating
Tires will also have other letters and numbers that indicate their performance. One such set of letters is the traction rating. The traction rating on tires determines how well it comes to a stop on a wet or otherwise un-dry surface. These letters start at AA (for the best) and go down to C (for the worst).
Temperature Rating
Tires can also have a temperature rating. When tires move quickly or spin they generate heat through friction. There are three ratings for temperature: A, B, and C. A is the best and C is the worst.
Treadwear Rating
Treadwear rating is represented by a number that’s based on 100. If a tire has a 200 that means the tire can last twice as long as an average tire. If a tire has a 50 that means it can last half as long as an average tire. Treadwear Rating numbers will typically be found after the word “Treadwear” is on the side of the tire.
While these are the most common letters and numbers found on the side of a tire, tires can have more depending on their design.
Tire Maintenance
Maintaining a tire can give it extra miles and save you money on replacement costs. There are several things needed to properly maintain a tire. Most of them are easy to do but some require the help of a mechanic.
Tire Rotation
Tire rotation is one of the most important parts of tire maintenance. Every 5,000-10,000 miles you should have your tires rotated. Tires need to be rotated because each wheel of the car has a different purpose. For example, cars with rear-wheel drive use the rear wheels to propel the car forward. This makes the rear tires wear down faster than the front tires. By rotating your tires you can prevent uneven tread wear.
Air Pressure
Making sure your tires have the right amount of air pressure is essential for optimal tire performance. Tires that don’t have adequate air pressure can become flat over time, which can lead to internal and external tire damage. Moreover, too much air pressure can create too much pressure that leads to popping and blowouts.
Most vehicles have a tire pressure sensor to alert you when tire pressure is too low or too high. That said, some older vehicles don’t have this technology. In these cases, you’ll have to use a tire pressure gauge to check the air pressure.
Tire Balance
When tires are placed on a vehicle weights are added to the tires. These weights balance the tire by removing small vibrations that occur when the vehicle turns or makes sudden changes in direction. Tires need to be balanced whenever new tires are added to your vehicle or whenever you remove a tire to repair the damage.
Wheel Alignment
Wheel alignment is another huge factor in tire maintenance. Every vehicle has unique wheel alignment needs, so you need to make sure your tires and wheels are aligned according to the specifications of your manufacturer. If any wheel or tire is not properly aligned it can wear down prematurely. You should always check your vehicle’s wheel alignment when new tires are installed or if you notice your vehicle drifting as you drive in a straight line.
If you maintain your tires properly you can extend the life of your vehicle’s tires by thousands of miles.
Wrapping Up
Tires are essential for your vehicle. They make your ride smooth, protect your wheels, and work together with your vehicle’s suspension to keep you on the road. That said, tires are more complicated than they seem. There is a lot to learn about tires, so it’s important to know what you’re looking at. The letters and numbers on the side of a tire can tell you everything you need to know about. It’s better to know more than less when shopping for tires.
Jed Lehman
Jed Lehman is a born gearhead who has been working on cars since he could crawl. He inherited his love for auto from his grandfather who owned a maintenance shop in Carlsbad, California. Jed is the driver behind Gearshift, and started this site to provide straightforward, helpful automobile information. From maintenance tips to product reviews, you can find it all here.
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