How to Read Tire Size and Understand Every Number on Your Tire

Learning How to Read Tire Size is one of those small car-care skills that can save you money, prevent confusion at the tire shop, and help you avoid buying the wrong set of tires online. I have seen many drivers look at a tire sidewall, see something like P225/60R17 98H, and immediately feel lost. Honestly, I understand why. At first glance, it looks like a random mix of letters and numbers.

But once you know what each part means, the code becomes surprisingly simple.

Your tire size tells you the tire type, width, sidewall height, construction, wheel diameter, load capacity, and speed rating. It also helps you confirm whether a replacement tire actually matches your vehicle. According to the National Highway Traffic Safety Administration, drivers should choose tires in the same size recommended by the vehicle manufacturer or another approved size listed in the owner’s manual or on the driver-side door label.

In this article, I’ll break down every number and letter in a tire size in plain English, using real examples you can check on your own car.

Why Tire Size Matters More Than Most Drivers Think

Tire size is not just a shopping detail. It affects safety, braking, fuel economy, ride comfort, steering response, and even how accurate your speedometer is.

When a tire is too wide, too tall, or too small for the vehicle, it can create problems such as:

• Poor handling
• Tire rubbing against the wheel well
• Incorrect speedometer readings
• Reduced fuel efficiency
• Faster suspension wear
• Poor braking performance
• Lower load-carrying safety

I always tell people this: tires are the only part of your vehicle that touch the road. That small contact patch carries the weight of the car, passengers, cargo, and every braking or turning force.

That is why knowing How to Read Tire Size is not just useful for car enthusiasts. It is practical knowledge for every driver.

Where to Find Your Tire Size

You can usually find your tire size in three places.

First, look at the sidewall of your current tire. The size is printed in raised letters and numbers around the outer side of the tire.

Second, check the sticker inside the driver-side door jamb. This label usually lists the factory-recommended tire size and proper tire pressure.

Third, look in your vehicle owner’s manual. This is especially helpful if the car has different tire options for different trims.

The NHTSA also advises checking the owner’s manual or the Tire and Loading Information Label on the driver-side door edge or post to find the correct tire size for your vehicle.

How to Read Tire Size on a Common Tire Code

Let’s use this example:

P225/60R17 98H

This is a common-looking tire size. Here is what each part means.

Tire Code Part	Meaning
P	Passenger vehicle tire
225	Tire width in millimeters
60	Aspect ratio or sidewall height percentage
R	Radial construction
17	Wheel diameter in inches
98	Load index
H	Speed rating

At first, it may look technical. But once you separate the code into parts, it becomes much easier to understand.

What the First Letter Means

The first letter tells you the tire class or intended vehicle type.

In the example P225/60R17, the P means the tire is a P-metric passenger tire. Bridgestone explains that “P” stands for P-metric and is commonly used for passenger vehicles such as cars, minivans, SUVs, and some light-duty pickups.

Common tire type letters include:

• P: Passenger vehicle tire
• LT: Light truck tire
• T: Temporary spare tire
• ST: Special trailer tire
• No letter: Euro-metric tire

If your tire size starts with LT, it is usually built for heavier loads, towing, or trucks. If it starts with T, it is a temporary spare and should not be treated like a regular tire.

This first letter is one of the easiest parts to overlook, but it matters. A tire designed for a passenger sedan is not the same as a tire built for a trailer or heavy-duty pickup.

What Tire Width Means

The first three-digit number shows the tire width in millimeters.

In P225/60R17, the number 225 means the tire is about 225 millimeters wide from sidewall to sidewall.

This is not the tread width only. It refers to the section width, which is measured across the tire’s widest point when mounted correctly.

A wider tire may provide more road contact, but wider is not always better. It can affect fuel economy, steering feel, road noise, and clearance.

For example:

• A 205 tire is narrower than a 225 tire.
• A 245 tire is wider than a 225 tire.
• A wider tire may need a compatible wheel width.

When learning How to Read Tire Size, this number is usually the first major clue to whether the tire will physically fit your vehicle.

What Aspect Ratio Means

The number after the slash is the aspect ratio.

In P225/60R17, the 60 means the tire’s sidewall height is 60 percent of the tire width.

So, if the tire width is 225 millimeters, the sidewall height is 60 percent of 225.

That equals 135 millimeters.

This number affects how the tire looks and feels on the road.

A higher aspect ratio means a taller sidewall. A lower aspect ratio means a shorter sidewall.

For example:

• 225/70R16 has a taller sidewall.
• 225/45R18 has a shorter sidewall.
• 225/35R19 looks sportier but may ride firmer.

Tall sidewalls usually provide more comfort because they absorb road bumps better. Short sidewalls often improve steering response, but they can make the ride feel harsher.

This is why sports cars often have low-profile tires, while SUVs and family vehicles usually have more sidewall.

What the “R” Means in Tire Size

The letter R means radial construction.

Most modern passenger vehicle tires use radial construction. In a radial tire, the internal layers run across the tire from bead to bead, helping improve durability, ride quality, and fuel efficiency.

You may occasionally see other letters, but R is by far the most common.

For most everyday drivers, you do not need to think too deeply about this part. Just make sure the replacement tire matches the same construction type recommended for your vehicle.

What Wheel Diameter Means

The number after the construction letter tells you the wheel diameter in inches.

In P225/60R17, the 17 means the tire fits a 17-inch wheel.

This is one of the most important numbers when replacing tires. A 17-inch tire will not fit a 16-inch wheel. A 16-inch tire will not fit an 18-inch wheel.

The wheel diameter must match exactly.

This number is different from the total height of the tire. It only refers to the rim size the tire is designed to fit.

A common mistake I see is when someone thinks a 225/60R17 and 225/60R18 are almost the same. They are not interchangeable because the wheel diameter is different.

What Load Index Means

After the main tire size, you will usually see a number such as 98.

In P225/60R17 98H, the 98 is the load index. It tells you how much weight each tire can safely carry when properly inflated.

The load index does not show the weight directly. It corresponds to a standardized chart.

For example, a load index of 98 generally means the tire can carry about 1,653 pounds per tire.

Load index is especially important if you drive an SUV, truck, minivan, or vehicle that often carries passengers, luggage, tools, or towing weight.

Bridgestone notes that the load index is typically shown beside the speed rating, such as “91S,” and indicates the weight the tire can support when properly inflated.

My practical advice is simple: never choose a tire with a lower load index than what your vehicle manufacturer recommends.

What Speed Rating Means

The final letter is the speed rating.

In P225/60R17 98H, the H is the speed rating. It shows the maximum speed capability of the tire under proper conditions.

Common speed ratings include:

Speed Rating	Maximum Speed
S	112 mph
T	118 mph
H	130 mph
V	149 mph
W	168 mph
Y	186 mph

This does not mean you should drive at those speeds. It simply indicates the tire’s tested speed capability.

Speed rating can also affect handling, heat resistance, and ride feel. A tire with a higher speed rating may have a firmer ride or sportier response.

For regular daily driving, choose the rating recommended by the vehicle manufacturer. Going lower can affect safety and performance.

How to Read Tire Size on Light Truck Tires

Light truck tires may look a little different.

Example:

LT265/70R17 121/118S

Here is what it means:

• LT means light truck
• 265 means 265 millimeters wide
• 70 means sidewall height is 70 percent of the width
• R means radial
• 17 means 17-inch wheel
• 121/118 means load index for single and dual-wheel use
• S means speed rating

Light truck tires are common on pickups, full-size SUVs, and vehicles used for towing or hauling.

You may also see tire sizes like:

35×12.50R17LT

This is a flotation-style tire size often used for trucks and off-road vehicles.

In that format:

• 35 is the overall tire diameter in inches
• 12.50 is the tire width in inches
• R means radial
• 17 is the wheel diameter in inches
• LT means light truck

This format is more common in off-road tire shopping.

What DOT Code Means on a Tire

The DOT code is different from the tire size, but it is also printed on the sidewall.

DOT stands for Department of Transportation. This code helps identify the tire manufacturer, plant, size, and production date.

The most important part for everyday drivers is the last four digits of the DOT code.

For example:

DOT XXXX XXXX 2624

The final four digits mean the tire was made in the 26th week of 2024.

The first two digits show the production week. The last two digits show the year.

The NHTSA states that standardized tire sidewall information identifies key tire characteristics and includes a tire identification number for safety certification and recalls.

This matters because tires age even if they look good. Rubber can dry out, crack, and lose performance over time.

How Old Is Too Old for a Tire?

There is no single age rule that fits every situation because heat, storage, driving habits, and climate all matter.

Still, many vehicle and tire experts recommend inspecting tires carefully as they age, especially after six years. If a tire is ten years old, it should be treated with serious caution even if tread remains.

When checking a used car or buying used tires, I always inspect the DOT date first. A tire with deep tread but an old date code may not be a good deal.

What UTQG Ratings Mean

Some tires also show UTQG ratings. UTQG stands for Uniform Tire Quality Grading.

It usually includes:

• Treadwear
• Traction
• Temperature

For example:

Treadwear 500 Traction A Temperature A

Treadwear gives a comparative idea of expected tread life. Traction grades relate to wet stopping performance. Temperature grades relate to heat resistance.

These ratings are useful, but they are not perfect. Different tire brands, driving styles, road conditions, and maintenance habits all affect real-world tire life.

Use UTQG as one comparison point, not the only decision-maker.

Tire Size Example: Breaking It Down Like a Mechanic

Let’s decode this tire:

P235/55R18 100V

Here is how I would read it:

P tells me it is made for passenger vehicles.

235 means the tire is 235 millimeters wide.

55 means the sidewall height is 55 percent of the tire width.

R means radial construction.

18 means it fits an 18-inch wheel.

100 is the load index.

V is the speed rating.

Before buying a replacement, I would compare this full size with the driver-side door label, not just the tire currently installed. Why? Because previous owners sometimes install the wrong size.

Why You Should Check the Door Label Before Buying Tires

This is one of my strongest tire-buying tips.

Do not rely only on the tire currently mounted on the car. Check the manufacturer label inside the driver-side door.

Why?

Because the current tire may not be original. A previous owner or shop may have installed a different size.

The door label usually tells you:

• Original tire size
• Recommended tire pressure
• Vehicle load information
• Front and rear tire pressure differences if applicable

If your tire size does not match the door label, do not panic. Some vehicles allow optional sizes. But you should confirm compatibility before buying replacements.

Can You Use a Different Tire Size?

Sometimes, yes. But it should be done carefully.

Changing tire size can affect:

• Speedometer accuracy
• ABS performance
• Traction control behavior
• Ride height
• Steering feel
• Fuel economy
• Fender clearance

A small size change may be acceptable if the overall diameter stays close to the original size. But random changes can create real problems.

For example, increasing wheel size while reducing sidewall height is common. This is called plus-sizing. A car may move from a 17-inch wheel to an 18-inch wheel while keeping the overall tire diameter similar.

But this should be calculated properly.

If you are not sure, ask a qualified tire professional before changing size.

Common Tire Size Mistakes I See

When people are learning How to Read Tire Size, they often make the same mistakes.

Mistake 1: Buying the Right Width but Wrong Wheel Size

A 225/60R17 and a 225/60R16 are not the same. The wheel diameter must match.

Mistake 2: Ignoring Load Index

A tire may physically fit but still be unsafe if the load index is too low.

Mistake 3: Choosing Tires Only by Price

Cheap tires can cost more in the long run if they wear quickly, ride poorly, or perform badly in rain.

Mistake 4: Mixing Different Tire Sizes

Some vehicles use staggered sizes, but many do not. Mixing sizes without knowing the vehicle design can affect stability and drivetrain components.

Mistake 5: Ignoring Tire Age

A tire may look fine but still be old. Always check the DOT date code.

How Tire Size Affects Fuel Economy

Tire size can influence fuel efficiency.

Wider tires may create more rolling resistance. Heavier tires can require more energy to move. Larger overall diameter can affect gearing and acceleration.

That does not mean bigger tires are always bad. It means tire choice should match your vehicle and driving needs.

For daily commuting, the factory size is usually the best balance of comfort, fuel economy, handling, and safety.

How Tire Size Affects Ride Comfort

Sidewall height has a big effect on comfort.

A taller sidewall absorbs bumps better. A shorter sidewall gives quicker steering response but transfers more road harshness into the cabin.

That is why a family SUV on 17-inch wheels may feel smoother than the same vehicle on 20-inch wheels with low-profile tires.

When someone asks me which tire size rides better, I usually look at the aspect ratio first.

How Tire Size Affects Handling

Tire width, sidewall height, and speed rating all affect handling.

A wider tire can improve grip in some conditions, but it can also increase road noise and reduce efficiency. A shorter sidewall can make steering feel sharper, but it may reduce comfort.

For performance cars, that tradeoff may be worth it. For daily drivers, balance matters more.

The best tire is not always the biggest or sportiest one. The best tire is the one that suits the vehicle, road conditions, and driver needs.

How to Read Tire Size Before Buying Online

Buying tires online can save money, but only if you enter the correct size.

Before ordering, check:

• Tire type letter
• Width
• Aspect ratio
• Construction letter
• Wheel diameter
• Load index
• Speed rating
• Vehicle manufacturer recommendation
• Seasonal tire type
• DOT date if available

Also confirm whether the price includes installation, balancing, valve stems, disposal fees, or road hazard coverage.

A tire that looks cheaper online may not be cheaper after installation costs.

What About Tire Pressure?

Tire size and tire pressure are related, but they are not the same thing.

The correct tire pressure is usually listed on the driver-side door label, not on the tire sidewall.

The number on the tire sidewall often shows maximum pressure, not the recommended daily driving pressure.

This is a common mistake. Do not inflate your tires to the maximum sidewall pressure unless instructed for a specific reason by the manufacturer or a qualified professional.

Correct tire pressure helps improve:

• Safety
• Fuel economy
• Tire life
• Braking
• Handling
• Ride quality

Simple Formula for Understanding Sidewall Height

Here is a quick way to understand sidewall height.

If your tire is 225/60R17:

225 × 0.60 = 135 mm

That means the sidewall height is about 135 millimeters.

If your tire is 225/45R17:

225 × 0.45 = 101.25 mm

That tire has a shorter sidewall, even though the width and wheel diameter are similar.

This is why the aspect ratio matters so much.

How to Read Tire Size for SUVs and Crossovers

SUVs and crossovers often use sizes like:

235/60R18

245/50R20

265/65R17

The same rules apply. Read the width first, then the aspect ratio, then the wheel size, then load and speed rating.

SUV owners should pay extra attention to load index. These vehicles are heavier than sedans and often carry more cargo or passengers.

If you tow, haul, or drive long distances, matching the proper load rating becomes even more important.

How to Read Tire Size for Winter Tires

Winter tires should also match the recommended size or an approved alternative.

Some drivers choose a slightly narrower winter tire because it can perform better in snow by cutting through slush more effectively. But this should still be done within approved fitment ranges.

Look for winter-related markings such as:

• M+S
• Snowflake mountain symbol
• Winter tire branding

A correct size with the wrong seasonal performance can still be a poor choice. Tire size tells you fitment. Tire type tells you purpose.

Quick Checklist Before Replacing Tires

Before you buy tires, use this quick checklist:

• Match the tire size on the door label
• Confirm wheel diameter exactly
• Match or exceed load index
• Match or exceed speed rating
• Check the DOT date code
• Choose the right season type
• Replace tires in proper pairs or sets
• Avoid mixing different tread patterns unless approved
• Confirm installation costs
• Ask about balancing and alignment

This checklist can prevent most tire-buying mistakes.

FAQs About How to Read Tire Size

What does 225 mean on a tire?

The number 225 means the tire is about 225 millimeters wide from sidewall to sidewall.

What does 60 mean in tire size?

The number 60 is the aspect ratio. It means the tire’s sidewall height is 60 percent of the tire width.

What does R mean on a tire?

The letter R means radial construction, which is the most common tire construction type used today.

What does 17 mean in tire size?

The number 17 means the tire fits a 17-inch wheel.

Can I put a different tire size on my car?

Sometimes you can, but it must be compatible with your vehicle. Always check the owner’s manual, door label, or a trusted tire professional before changing sizes.

Is load index important?

Yes. The load index tells you how much weight the tire can safely carry when properly inflated. Never use a tire with a lower load index than recommended.

Is speed rating important for normal driving?

Yes, because speed rating can also relate to tire construction, heat resistance, and handling. Use the rating recommended by your vehicle manufacturer.

Conclusion

Knowing How to Read Tire Size gives you more control when buying tires, checking your vehicle, or talking with a tire shop. The code on your sidewall may look confusing at first, but each part has a clear purpose.

Start with the tire type, then read the width, aspect ratio, construction, wheel diameter, load index, and speed rating. Once you understand that pattern, a size like P225/60R17 98H no longer feels intimidating.

My final advice is simple: always compare your tire size with the driver-side door label, not just the tire currently on the car. Match the wheel diameter exactly, never ignore load index, and check the DOT date before buying.

Tires affect comfort, braking, fuel economy, and road safety every time you drive. A few minutes spent reading the sidewall can help you make a smarter, safer purchase. For readers who want to study the broader technical background, the tire code system gives a useful overview of how these markings are organized.