Kelley Blue Book: Which tires should you buy? Here’s a complete guide.

When they need replacing, a tire shop or dealership can seem intimidating with dozens of types on the wall and an employee at a computer with a database of even more choices.

Also read: These are the cars that cost the most and least to insure

We’ll walk you through the basics of tires and help you understand these circles of rubber that keep you on the road. We’ll provide all the basics, including all the types of tires available and the numbers behind them.

Types of tires

The bad news — there are at least six types of tires common enough that the average tire shop generally has them in stock. The good news — almost everyone needs the same type.

In a few climates, it helps to know about a second type of tire. The rest are for people who buy specialized vehicles. So, most of us can skip them. If you’re shopping for a performance car or a vehicle you’re going to take off-road, you will need to learn a few more terms. But people buying those types of cars expect the need for a bit of special knowledge.

You might like: What is EV, BEV, HEV, PHEV? Here’s your guide to types of electric cars

The better news — the company that built your car almost certainly shipped it to you with the best tire choice for your vehicle. All you need to do is avoid big changes to keep things rolling.

All-season tires

All-season tires work like the casual shoes of the car world. They must do most things well that people need them to do. They provide a good combination of safe traction in most weather conditions, reasonably low noise, and long life at a moderate price.

Most cars come from the factory wearing all-season tires. When all-season tires wear out, most people get another set and go on driving safely. They are usually sold according to how many miles they are expected to last in normal driving.

High-performance all-season tires

These are the cross trainers of tires. They come standard on many sports cars. Their rubber is a bit softer than what’s used to make standard all-season tires, so they grip the road a bit more. But they last about two-thirds as long as the more common all-season tires and cost a bit more. Could you improve your family sedan’s performance with a grippier set of high-performance all-season tires? Probably. But you’d spend more up front and have to spend it again sooner.

High-performance summer tires

The halfway point between an all-season tire and a racing tire, high-performance summer tires are like good running shoes for your car. But this is where our shoe analogy falls apart.

Changing your shoes several times a day is no big deal. Changing your tires several times a season is time-consuming and costly. In mild climates, high-performance tires may serve all summer long. But when steady rain or any snow is a possibility, they won’t do. So most consumers don’t buy them or only use them on a sports car kept around as a second vehicle. They are rarely the right choice on a daily driver.

These are faster and built of softer and stickier rubber than all-season tires. They’re safe enough in light rain, but lose traction in heavier storms, and are simply unsafe in cold weather.

Ultra-high-performance summer tires/track tires/racing slicks

Sticking with our shoe analogy after it fell apart, these are the highly specialized track shoes you see Olympians running in. Ever notice how those athletes put their shoes on after they step on the track, and take them off before they step off it? They do that because they’re not practical for walking around in, and to preserve them because they are pricey.

Check out: Onyx, nightfall, midnight—call it what you want, black is the new black in cars

The highest-performance tires are much the same. Soft and sticky, they will make an exotic car or highly tuned race car stick to a smooth track even against the G-forces generated in a hard turn at high speed. They can cost more than double the amount of an all-season tire. More importantly, from a cost standpoint, they wear so quickly that tire manufacturers often don’t bother putting a mileage rating on them. Most readers will never have a good reason to invest in a set of ultra-high-performance summer tires.

Winter tires

Winter tires work like the snow boots of the tire world. They’re a fantastic idea if you live where snow regularly falls when you’re trying to get around. They use rubber compounds formulated to grip well even when frozen, and deeper lug patterns that let them grip in slush. All-season tires are enough for you if you live where snow happens infrequently. But if you live where snow affects your driving often, you’ll want to invest in a set of winter tires.

Consumer Reports testing has even shown that, in some circumstances, a front-wheel-drive (FWD) car with winter tires has more traction in the snow than an all-wheel-drive (AWD) car with all-season tires. Since AWD systems can add thousands to the cost of a new car, many consumers might save money and drive safer in the snow by choosing winter tires instead. Of course, an AWD car with snow tires works like the grippiest of grippy cars in a winter storm.

If you buy winter tires, you’ll want to change them when the weather gets warm. The same rubber formulas that hold up well in the cold wear fast in warmer weather. Driving on your snow tires in spring or summer will just wear them out quickly.

Also read: What to expect when returning a leased car

If you choose to own one set of tires for winter and another for the other three seasons, many tire shops will happily store the set you’re not using for a small fee. After all, that means you’re coming back to pay them to swap them out again.

All-terrain tires

All-terrain tires are the hiking boots of the automotive world. Typically found on trucks and SUVs, they have much deeper lug patterns to retain grip even in the mud.

Can you add all-terrain tires to your compact sedan to give it off-road chops? Probably not without making a lot of other expensive changes first. Tire shops usually stock them only in the larger sizes needed for trucks and SUVs. So you’d need larger wheels, not just larger tires.

All-terrain tires sound noisier than other tires and provide a bumpy, hard ride on smooth roads. But they’re the only choice if you’re outfitting your Ford F, +11.67% Raptor, Jeep Wrangler, or other off-road-oriented rides.

Run-flat tires

Run-flats are not actually a separate category of tire. High-performance, all-season, and winter tires are available in run-flat styles. A run-flat tire has an internal support structure that allows it to continue driving safely for a certain distance even after it has been pierced. Run-flat tires, however, cannot drive at all speeds or indefinitely after losing air. They are designed to get you safely to a place where you can have the tire repaired or replaced.

Many luxury vehicles today come equipped with run-flat tires. Some even lack the accommodations to mount a spare tire, requiring that drivers replace their run-flats with more run flats when they wear out.

Also see: Avoid these 10 common mistakes when buying car insurance

Run-flat tires cost more than ordinary tires but can give drivers peace of mind. They can be slightly noisier than ordinary tires and give a slightly rougher ride. But many drivers find the changes undetectable.

Airless tires

While the types of tires above use air, Michelin is developing a new concept aluminum tire that is not only airless but puncture-proof as well. Michelin expects its airless tires to hit the car market in 2024. Bridgestone, too, is working on producing airless tires for the car market.

Airless tires, already in use on golf carts, would be revolutionary for cars. Using tires that require no air, eliminates flat tires and costs associated with them. Both companies announced that their tires will be eco-conscious as they will be made from recycled material.

How to read the markings on a tire

Everything you need to know about a set of tires is written on the sidewall of the tire itself. But there’s usually no table to explain what you’re looking at. A code indicates the various sizes and ratings of the tire.

The code follows a pattern like the following:

Tire Type| Tire Width/Aspect Ratio | Tire Construction | Wheel Diameter | Load Index | Speed Rating

Here’s how to break down this example:

P 225/45 R 18 95 H

P

The “P” in this example stands for Passenger. If you’re not driving a commercial vehicle, you’re likely to encounter only Passenger (P) and Light Truck (LT) tires.

225

This is the tire’s width in millimeters. It is possible to mount tires of a different width to your vehicle than those that came with your car. But that will change the car’s handling and require other expensive adjustments (more on that in a moment).

45

The 45 is the ratio of the tire’s height to its width. In this example, the height is 45% of the tire’s width.

R

The means the tire is built with radial construction. The cords of rubber were laid out radially, 90 degrees from the direction of travel. Almost all tires used in passenger vehicles are built this way. Bias-ply tires (with the cords crisscrossed over one another) are sometimes seen in trailer tires.

18

This number is the diameter of the wheel the tire is mounted on, in inches.

95

The figure here lists the tire’s load index — a measure engineers use to show the maximum amount of weight the tire can support when fully inflated. Tires with a load index of 95 can hold up to 1,521 pounds.

H

This letter stands for the tire’s speed rating — the maximum speed the tire can safely travel according to the manufacturer. A speed rating of H means this tire can travel up to 130 mph.

Watch: How to balance saving for retirement and life in your 30s

Tire terms

You may encounter some of the following terms, and we define them so you’ll be prepared when tire shopping.

Air pressure

A measure of the pressure exerted outward on your tires by the gas contained inside them. Most tires are filled with air. Some luxury and high-performance car manufacturers prefer to fill tires with nitrogen, which escapes naturally through the pores in rubber more slowly than air. But nitrogen and compressed air perform roughly the same in tires. It’s fine to top off a nitrogen-filled tire with compressed air as needed.

Load index

A numerical code that shows how much weight a tire can support when properly inflated. Casual drivers do not need to memorize the load index scale to buy tires safely.

Manufacture date code

All tires built after the year 2000 include a date code showing when they were manufactured. The first two digits of the code indicate what week of the year a tire got made. The last two digits show the year.

Speed rating

An alphabetical code number showing the maximum speed a tire can drive safely. Casual drivers do not need to memorize the speed rating scale to buy tires effectively.

Tire pressure monitoring system

Modern cars have sensors that track air pressure within the tires and will activate a light or symbol in the driver’s instrument cluster to warn if a tire is low.

Traction rating

The U.S. Department of Transportation requires that tires carry a coded rating determined by a traction test on a wet surface. Tires are graded from AA (best) to C (worst) on how well they maintain traction during a straight-line braking test.

Also see: New to investing and not sure how to start? Try this approach

Temperature rating

The same set of regulations require a code showing the speed at which a tire can become too hot to function properly. All tires sold in the U.S. are rated to function properly at least 85 mph (a rating of C).

Treadwear grade

DOT regulations require that tires carry a code showing the rate at which their tread wears compared with a standardized test tire. A grade of 100 means the tire should last as long as the standardized test tire. A grade of 200 means it should last twice as long. Tire manufacturers have frequently complained that this test is not particularly useful, and few consumers know what it means.

Treadlife warranty

Many tires come with a warranty promising that they will last a certain number of miles under ordinary driving conditions. These warranties can be useful to give you a ballpark understanding of how long a particular tire may last. But should your tires fail early, they can be difficult to collect on and only pay out a small percentage of the original purchase price.

Does tire size matter?

Automakers engineer each car to work with a specific size and type of tire. It is possible to mount tires of a different size than your car was designed for, but you should do so only with the knowledge that you are changing how well your car will function.

Changing your tires’ width or aspect ratio can cause obvious problems like tires that rub against the suspension. It can also cause invisible problems — adding more wear and tear to the transmission and engine, changing the amount of weight a truck can carry or tow, or even making your speedometer inaccurate or your anti-lock brakes ineffective.

Of course, you’ve probably seen off-road vehicles or muscle cars with nonstandard tire sizes on the road. It is possible to safely make those changes.

Larger tires on a truck or off-road SUV can improve the vehicle’s ground clearance and change the approach, departure, and breakover angles that drivers need to know to get out of tough spots when rock crawling.

Wider tires on the rear wheels of a rear-wheel-drive performance car can give it a faster start, useful for short, straight-line spurts of speed like those in drag racing. But the added weight and grip can make a car’s fuel economy worse.

A reputable shop can safely put tires of a different size on most cars. But it takes a lot more work, and costs a great deal more than simply buying the new tires themselves. It can evolve by replacing the wheels the tires ride on, changing brake components, altering the differential on an AWD or 4-wheel-drive vehicle, and reprogramming or swapping out a car’s computers to ensure that critical safety functions aren’t compromised.

Those buying a vehicle for a specific use, like off-roading or drag racing, may find that cost worthwhile. It’s probably wasted on your daily driver.

When should you replace your tires?

You should replace your tires when they are too damaged, too worn, or too old to drive safely.

It’s easy to repair most minor tire damage caused by running over nails or screws. A tire shop, or a home mechanic with a few basic skills, can plug a puncture hole in a tire, often for less than $ 20.

But damage to a tire’s sidewall can threaten the structure of a tire. That kind of damage can occur if you brush up against a curb at high speed or run over an object at an awkward angle. A tire with a weak or damaged sidewall must be replaced to avoid a dangerous blowout.

Also on MarketWatch: These 5 great, easy-to-read books about money will change how you think about investing

Most tires are considered too worn to drive on at all when the tread is less than 1/16 of an inch. So you should replace them before they get to that point. We recommend tire shopping when the tread depth on your tires reaches 1/8 of an inch.

There’s a remarkably easy test for this: Fit a quarter in the central groove of tread, with George Washington facing you, and the top of his head pointed toward the center of the tire. If you can see the top of his head, you have less than 1/8 of an inch of tread depth left, and it’s time to start tire shopping at your local automotive dealership service department or tire retailer.

A similar test using a penny is not a reliable measure of safety. If you can see the top of Abe Lincoln’s head, you have less than 1/16 of an inch of tread depth left, and your tires are unsafe to use. Replace them immediately.

Rubber loses strength over time, even sitting unused. You should replace tires over 6 years old, even if they have plenty of tread left.

Should you replace all four tires at once?

If you get one flat tire, do you really need to buy four new ones?

This depends on the condition of your other tires, and the type of vehicle you are driving. If your tires are relatively new and still have much of their tread intact, you can usually get away with buying one tire of the same or a very similar model to replace the damaged one.

However, if you get a flat while driving on an older set of tires, the safest approach may be to replace them all. Having inconsistent traction levels on each corner of the car could be dangerous.

Some AWD vehicles require that you replace all four tires at once. In an AWD vehicle, the reduced diameter of a lower-tread tire may cause it to spin faster than a new tire. AWD vehicles are designed to move the wheels at different speeds for short periods to provide the most traction possible. But their components can wear out quickly or be damaged trying to compensate for mismatched tires for days at a time.

Are used tires worth the savings?

About 10% of the tires sold in America each year are used. While it’s possible to buy a used tire that’s safe, we strongly caution against it for one simple reason: Used tires are almost entirely unregulated in the U.S. There is simply no way to verify whether a used tire shop is lying about the condition or age of its products.

That means there’s no agency verifying that the tires you buy used are safe, and you have almost no recourse as a consumer if they fail. What’s worse is if the used tires fail and cause a fatal accident.

Checking for tire recalls

The DOT regulates tire production and sales and tracks complaints about brands and tire models. Sometimes, regulations require a manufacturer to recall defective tires and repair or replace them.

Use this research tool to check for any manufacturer recalls on your car. Recall repairs are always free.

Many cars may be subject to a recall at some point in their lives. By law, manufacturers reach out to owners by mail to notify them of recalls. However, they don’t necessarily have accurate addresses for everyone.

Rotation, alignment, and tire maintenance

To ensure the maximum life for your tires, you must maintain them. This occasionally requires that you spend money on minor tire services. But, done properly, this should save you money over time. Properly maintaining your tires is a lot less expensive than replacing them often because they weren’t properly maintained.

There are three common maintenance procedures for tires:

Tire rotation

Tire rotation doesn’t refer to spinning your tires, but rather dismounting them and remounting them on different wheels. Front tires and back tires wear differently, as front tires steer your car. To keep them wearing consistently, you must move the back tires to the front and the front tires to the back on a regular schedule.

You can find the schedule in your car’s owner’s manual. Most manufacturers suggest a tire rotation about every 7,000 miles. Use this car maintenance tool to determine what other types of interval service you may need for your car.

A tire rotation generally costs less than $ 120. KBB’s auto repair pricing tool can give you a more precise estimate for your make and model.

Note: Some sports cars or other special-use vehicles have different tires on the front and rear axles. Your car’s owner’s manual will tell you what to do in this case.

Wheel alignment

When your car left the factory, its wheels were pointed in the same direction. Over tens of thousands of miles of driving, turning, and hitting potholes, the many moving joints in your car’s suspension and steering may have moved subtly out of alignment. It is often necessary to have a mechanic adjust them to ensure that they point in the same direction.

Most manufacturers recommend a wheel alignment every six months or 6,000 miles, or any time you get new tires. An alignment generally costs $ 100 or less.

Check our Service and Repair Guide to find out how much a wheel alignment costs for your vehicle.

Tire balancing

On fitting new tires, a shop will install small weights inside the wheels to limit vibration. Tires should be rebalanced every time they are dismounted and remounted and can be rebalanced to stop a vibration if you notice one while driving. A tire balancing service generally costs $ 75 or less.

All about tire pressure

It’s important to keep your car’s tires near a specific pressure rating to perform safely. This pressure rating is usually found on a placard on the inside driver’s door for easy reference.

Since 2007, federal law has required all passenger cars sold in the U.S. to have a Tire Pressure Monitoring System (TPSM) that alerts drivers when tire pressure is low. In older cars, it’s a good idea to check tire pressure with a simple, inexpensive gauge at least once a month.

Tires will gain or lose pressure naturally as the weather changes, requiring you to top off the pressure occasionally. This is easy to do with the air compressors found at many gas stations.

One note of caution — most gas station air compressors have a pressure gauge mounted to the nozzle, but we don’t recommend trusting it. Since these are used repeatedly by dozens of people each day and rarely replaced, they are often worn and inaccurate. It’s best to refill the air with the compressor, but check the pressure with a gauge you keep in your own glove box for this purpose.

Improperly inflated tires are dangerous. Underinflated tires have too much of their surface in contact with the road, which can cause them to overheat. Even in a best-case scenario, underinflated tires wear more quickly than they’re designed to. In a worst-case scenario, they can heat up while driving and burst.

Overinflated tires have too little contact with the road. They can lose traction, making your car difficult to control. They can increase braking distance, making you more likely to slide into the car in front of you.

Also read: Why you might not make it to the next gas station

How to make your tires last longer

The treadwear warranty says that your new tires should last 70,000 miles. But that warranty assumes that you will care for them properly.

They will last 70,000 miles if you keep them inflated to the proper pressure for your car, have them rotated and aligned according to the schedule in your car’s owner’s manual, and get them rebalanced any time you notice a strange vibration.

How to change a flat tire

Even if you care for your tires perfectly, you may still run over a nail, hit a pothole, or otherwise find yourself driving on a flat tire.

If your car is equipped with run-flat tires instead of a spare tire, simply drive to a shop that can replace the tire for you.

If your car comes equipped with a spare tire, you must know how to mount it safely.

Thankfully, you can change your flat tire in seven easy steps.

1. Get to a safe place

Drive to level, solid ground, safely out of traffic. You must remain on a flat, paved surface. On an uneven surface, your car may fall off the jack. On a soft surface, the jack will simply sink into the ground instead of lifting the car.

Set the parking brake for safety even if you don’t usually use it to park.

2. Find the spare, lug wrench, and jack

A spare tire and the equipment needed to use it are usually located beneath the carpet in the trunk of a car or under the cargo area of an SUV. On some pickup trucks and minivans, they are mounted beneath the rear of the vehicle.

With the spare, you’ll find a large lug wrench, and a jack to lift the side of the car with the flat.

Related: Keeping these things in your car will prepare you for almost any emergency

3. Loosen the lug nuts on the flat tire

While the tire is still on the ground, use the lug wrench to slightly loosen each nut. The nuts are often rusted or fused in place. It will be easier to loosen the nuts before raising the car on the jack, while the tire cannot spin.

4. Raise the car with the jack

Underneath your car, there will be specific jack points designed to accommodate the jack. They are usually marked with arrows. Place the jack under the jack point nearest the flat tire and turn the crank to raise the car. Stop as soon as the flat tire is off the ground — it’s not usually necessary or helpful to use the full height of the jack.

5. Remove the nuts and the wheel

Remove the nuts with the lug wrench and place them nearby on a flat surface so they won’t roll away. Then, pull the flat tire off the car and set it aside.

On rare occasions, the wheel may have rusted to the wheel hub. If you cannot lift it off, lower the jack slightly so that just a little of the car’s weight settles onto the wheel with the lug nuts removed, breaking any seal. Then raise it again and remove the wheel.

6. Replace it with the spare

Lift the spare tire into place and screw the lug nuts back on, tightening them by hand. Tighten them with the lug wrench, but do not make them as tight as possible.

7. Lower the jack and tighten again

Lower the car until the jack is not supporting it at all. Remove the jack. Then, tighten the lug nuts a final time with the wrench. If there are four or six, tighten them in opposing pairs. If there are five, tighten every other nut, moving between them in a clockwise fashion, until you’ve tightened them all.

Now, put the flat tire, jack, and lug wrench in the trunk.

Check out: Recycling is confusing — how to be smarter about all that takeout plastic

Your spare tire will have a warning on it with a maximum speed — usually around 45 mph. Drive to a repair shop, not exceeding this speed, to repair or replace the flat.

This story originally ran on KBB.com.