How to choose a fitting tire size

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Tires keep direct contact with the road and can affect how a vehicle performs. So while shopping for replacement tires, other than tire types, speed ratings, and conditions it will be driven, getting the right size should get vital consideration.

Anything too big or too small will negatively impact vehicle performance, give drivability issues and even compromise safety. Hence, the need to get only the right tire sizes. This has, however, led to many asking what size tires fit my car. We will answer this question, but first, let’s get an in-depth understanding of tire sizes.

Tire size explained

In finding the right tire sizes, the most important parameter is the width, aspect ratio, and rim diameter. However, to get the right tires that suit your vehicle type and driving conditions, we will explain all. In explaining this, we will use a random tire size—P255/50/R17 98H. So what do these letters and numbers mean?

The first letter

This letter usually comes first before any number and indicates the tire type. Tire type tells what tire class it is; that is vehicles it is built for. In the tire size, P255/50/R17 98H, the P here indicates the passenger vehicle tire. This means that this particular tire is built for passenger vehicles like cars, crossovers, SUVs, minivans, and light pickup trucks.

In some tires, the letter may come as LT, ST, or T.  LT stands for light truck tires. These tires are built for moving heavy loads and towing trailers. They are also suitable for people who desire an extra heavy-duty alternative. You will see them mostly outfitted to 3-quarter or 1-ton SUVs and trucks.

ST, on the other hand, means special trailers and are designed for use in trailers. This includes the fifth wheel and travel trailers as well as utility and boat trailers. In contrast, T means temporary. So if T comes as the first letter, the tire is built to be used as a spare tire.

Note: if no letter comes before the first number, such metric tires are usually referred to as European-sized tires. Its measurement is done in millimeters, but its load capacity may differ from LT or P tires.

Width

The width of a tire: P255/50/R17 98H, is the first number or the three-digit number that comes immediately after the first letter. Tire width, also called section width, is the sidewall-to-sidewall measurement of the tire in millimetres. So in this tire size information—”P255, the width is 255 millimetres wide and, of course, designed for passenger cars.

Aspect ratio

The number that comes after the first slash is the aspect ratio. It tells how tall your tire profile is. Aspect ratios are measured in percentage and are gotten by dividing the tire’s sidewall by its width.

In the example—P255/50/R17 98H, the aspect ratio is 50, meaning the tire’s height is 50% of its width.

To get this tire’s sidewall height in inches, convert its width of 255mm to inches and multiply your answer by 50% (0.50).

Tires with lower aspect ratios, such as the 50 series, provide better handling than those with higher aspect ratios, like the 70 and 75 series.

Construction type

The single letter after the second number or aspect ratio is the tire’s construction type and indicates the tire’s inner construction. In this tire size, P255/50/R17 98H, “R” is the inner construction of the tire and gives you a general view of the tire’s stability. There are two types of construction you will mostly see on tires—R and D.

R stands for radial tires. Radial tires feature a construction where the tire’s internal cords are positioned in a radial direction. Radial tires are the industry standard for most cars and have been so for more than 40 years. You will see the letter R on most tires.  Radial tires offer better grip, comfort, longer life span, and low rolling resistance, which accounts for better fuel mileage.

D, on the other hand, represents tires whose internal construction features diagonal pliers called bias. Bias ply tires are the oldest and were outfitted to vehicles and light trucks until the 70s. However, this internal construction may still be found on some motorcycles and trailers.

Rim diameter

The number that comes after the construction type is the tire’s rim diameter. It denotes the rim size the tire will fit perfectly. In this tire—P255/50/R17 98H, the rim diameter is 17, meaning this tire is built for vehicles with a 17-inch wheel.

This means that if you decide to change your rim to a higher size, you would also need to change your tires. A tire built for a 15-inch wheel will not fit properly into a 17-inch wheel. Even if you try, the tires may be too stretched, causing drivability issues.

Load Index

The load index is the number after the rim size and connotes the amount of load in pounds the tires can withstand when fully inflated. In our example—P255/50/R17 98H, the load index here is 98.

But don’t get this twisted. The load index does not state the exact number of weights it can support; instead, it corresponds to a load capacity listed on the index. Here is a tire chart showing the load index and corresponding load capacities.

From our example, P255/50/R17 98H, the load index—98 has a corresponding load capacity of 1653. This means this tire can support a load with a total weight of 1653 pounds.

Speed rating

The last letter is the speed rating and denotes the maximum speed capacity the tire can attain without compromising safety. In our example, P255/50/R17 98H, the speed rating is H., And H-rated tires are built to travel 130mph. Knowing this is important as it helps you control how fast you go for your safety.

It’s worth noting that your replacement tire’s speed rating must be the same or higher than the previous tires to maintain speed capacity. Also note that if your vehicle is outfitted with tires of different speed ratings, the slowest speed-rated tire will determine the vehicle’s maximum speed.

You may not find these letters in some tires since it’s not a must by law to add it. So you will need to check your owners manual regarding your model’s OEM speed rating if not listed in your factory tires.

In other tires, the speed ratings can be lettered S, T, W, Y, and some even come with two letters. These letters all have the speed they can attain according to manufacturer standards. Here is a tire speed chart showing the different letters and their corresponding top speed.

Note: Tires whose maximum speed rating is above 149mph may have a Zr placed in the speed rating symbol. For tires whose speed capacity exceeds 186mph, they may have a Zr attached with the symbol “Y” in a bracket.

What tire size fits my car?

If you’re opting for a replacement tire, you may ask, how do I know what size tires will fit my car? The tire size that will fit your car depends on your wheel size. Vehicle manufacturers place certain wheel and tire sizes in cars for specific reasons. It could be to boost fuel economy, handling, steering response, or other things to make a driving experience expedient.

So, for this reason, the tire size that will fit your car will be the tire size that came stock with the vehicle. You can find this information in your owner’s manual or under the centre console. You can also find your tire size information inside the fuel door or by the driver’s door frame or passenger door jamb (for older models).

Wondering where to find tire size on door? It’s simple, it is written on a sticker placed on these doors. That said, tire sizes that fit specific cars also come in ranges and are listed by vehicle manufacturers. So while the stock tire size is the manufacturer-recommended size, you could go lower or higher during replacement, following only your manufacturer’s recommendation.

Users may need to get bigger tires to suit their driving habits or make their vehicles more attractive. However, ensure you stay in the recommended tire range, which is stated in your vehicle tire chart. Getting too big or small tires may damage your vehicle and compromise safety.

Again, while making these modifications, ensure you understand how to read tire sizes, which we’ve already explained above. This makes sure you understand the difference between your previous tires and the modifications you’re making so you don’t go under or overboard with.  

Technology has even made it much simpler to find the best-fit tire size for your car. There are simple online tools like online calculators which not only show the best fit for your car but also give tire recommendations that tally with your choice, driving styles, and budget.

In using the tire size calculator, your model and make, sidewall numbers, or VIN may be needed. So you could find your tire size by VIN, using your make and model or the information on the original tire’s sidewall with the help of this calculator.

So technically, no matter what car you use, you can find the tire that fits using the above methods. So if you’re wondering, what size tires fit my 2012 Dodge Grand Caravan? Explore the options explained above to find the best tire sizes for your car.

How do I know what tire size fits my car?

For those going for replacement tires, you may ask, how do I know which tires fit my car? To know what tire sizes fit your car, look for the factory size. This information is in the owner’s manual, the tire itself, inside your fuel door, or the sticker on the driver’s door frame. Tire charts also show a range of tire sizes that can fit your car. Check the tire chart for your specific vehicle.

You could use the tire finder. The tire finder is a tire calculator that helps find the best fit for your application. So how do you use this tire finder? You could use your vehicle’s information or the numbers on your stock tire’s sidewall. The vehicle information needed includes the year, model, and version/option, which you would find in your manual or the sticker on the window or driver’s door jam.

If you’re using your tire’s sidewall number, all the calculator needs are the width, aspect ratio, and rim. Meaning you should be able to read your tire numbers. Using the tire size— P255/50/R17 98H, 255 is the width, 50 the aspect ratio, while 17 is the rim measured in inches. For full detail on reading tire numbers, scroll up. We already explained how to read tire numbers.

Frequently Asked Questions-FAQs

How do you know how big of tires you can fit?

While the tire that came with your car is the manufacturer’s recommended size, you could upsize. Some users go for a bigger size to boost traction, for aesthetics, to suit wheel sizes changed, etc. Whatever your reason is, you don’t want to go overboard, as certain tires might damage your suspension and other car components and even cause drivability issues.

So how do you know how big of a tire can fit? Start with your vehicle tire chart. It shows a range of tires that can fit your specific car. So long you’re using the same wheel, don’t go beyond the highest tire size recommended by your manufacturer.

Check your tire chart by vehicle, as the tire chart for a Toyota Corolla differs from that of an SUV. Online tire calculators also help in giving you ranges of tires that can fit. These calculators only require any of the following: VIN, vehicle make, year and model, or the numbers on your original tire’s sidewall.

Can I put different size tires on my car?

For better performance and safety, vehicle manufacturers recommend all tires outfitted to your car are of the same sizes. This allows for equal load index and speed rating on both the front and rear tires, creating a balance. But can I put different size tires on my car? Yes, you can, but not without conditions.

When mixing tire sizes, you must know your manufacturer’s size recommendation.  This is to ensure you don’t go way too much. The recommended tire size range that can fit your car is found on the vehicle tire chart. For example, if the recommended tire width is between 285 and 315, the tire sizes should be within this range. Maybe, a size 305 at the front and 315 at the back.

Again, use the same sizes for the wheels. For example, if you’re using a 305 for the front wheel, use it for both front wheels and vice versa for balance. That said, while using different tire sizes is possible, it might impact your load index, speed rating, durability, etc., which invariably affects performance and lifespan.

What size rims and tires will fit my car?

If you’re opting to replace your wheels and tires, you may ask, what size wheels and tires fit my car? What size rims and tires will fit your car depends solely on your vehicle’s make and model. Generally, there is the manufacturer-recommended rim and tire size for every car which come stock with the car.

To get your factory tire and wheel size information, look through your owner’s manual or the sticker on the driver’s door frame. Your original tire’s sidewall also has this information. That said, outside the recommended size, there is always room to increase or decrease wheel and tire size. And this is where the manufacturer tire chart comes in.

It shows a range of tire and rim sizes to fit your car. You can also use online calculators to make wheel and tire size comparisons to see which is best for you. The calculator may require you to input either your VIN, stock tire numbers, or your vehicle make, year, and model. For those asking, can I use this same process for wheels, and what size tires fit my truck? Yes, it is the same for all vehicles.

Can I replace 16-inch wheels with 18-inch?

You can replace a 16-inch rim with an 18-inch rim; it will give a smoother ride, awesome handling, and an amazing look. However, there are things to take into consideration before doing so. First, ensure you get a lightweight 18-inch rim, as it helps the suspension in doing its work and also improves the ride even with a low-profile tire. It also prevents you from getting thumps whenever you hit curbs.

Also, ensure the offset and width of the 18-inch wheel is not too different from the stock 16-inch. Else, your wheel may rub on your suspension. Thirdly, you will also need a tire size change. If you used a 16-inch rim, you probably used a 16-inch tire too. So now you need to upgrade to 18-inch tires, or else you may get a tougher ride.

Also, note that the new tires need a lower profile (sidewall height) to maintain sufficient clearance for road bumps and hazards. When a wheel’s diameter increases, there should also be a decrease in the tire’s height. For example, if your factory tire is 255/55/16  and you change to an 18-inch wheel, the correct tire to buy will be 235/40/18. Online calculators may also come in handy.

Do tire sizes need to be exact?

When we talk about tire size, different parameters are involved. But the most important ones you must consider are the width, aspect ratio, and rim diameter, as they affect a car’s performance. So whether tire sizes need to be exact depends on which parameter you’re talking about.

For the width and aspect ratio, they don’t always need to be exact. You could go a bit lower or higher, but avoid excess downsizing or upsizing. However, when it comes to the diameter, it must precisely match your rim’s diameter. For example, if your stock tires were 185/65R15, you can upsize to 195/70R15.

From the above example, the width of 185 was upsized to 195, while the aspect ratio of 65 was upsized to 70. However, the diameter of 15 inches remained the same.  Except you’re also changing wheel sizes; when changing tire size on the same rim, the tires and wheel’s diameter must be the same.

Is it better to have wider or taller tires?

Both tires have their advantages and flaws. Wider tires no doubt have larger contact patches and therefore have better hold on the road, so on dry roads, it provides better grip than tall tires. On wet roads, taller tires are resistant to hydroplaning, so they have a lower risk of hydroplaning than wider tires.

In extreme weather conditions, taller tires perform better as they offer more surface pressure against the road. Taller tires are also less costly and have lower noise and vibration with lower oil consumption. In contrast, wider tires offer better handling, cornering stability, improved turning radius, acceleration, and stopping power than tall tires.

Wider tires are a good fit for performance vehicles, whereas tall tires are good for regular cars. Wider tires will also change your car’s look to that wow look than tall tires. Wider tires are known to have high rolling resistance, which accounts for higher fuel consumption. So which is better for you depends on your driving conditions, desired look, driving habits, and vehicle type.

Do bigger or smaller tires go faster?

Smaller tires go faster but will cover a smaller distance for every tire revolution.  But while bigger tires will go slower, they cover a larger distance per wheel revolution. Generally, how slow or fast an object goes depends on the rotational moment of inertia. Moment of inertia typically means how easy or quickly an object can move.

Smaller tires have lower moments of inertia, while bigger tires have higher moments of inertia. Here is why. Smaller tires are light weighted, so they are easy to move from one point to another. It also allows the wheel to spin faster. Hence, the faster speed.

Bigger tires, on the other hand, are heavier, making them harder to move, accounting for their slower speeds. Bigger wheels also impact engine response and decrease the driving force. Decreased driving Force will, in turn, impact speed and acceleration.

How do you know what tires will fit my rims?

When changing tires, you must be sure that the tire size matches your wheel size. So, how do you know what tires fit my rims? Check your rim’s size and match it with the corresponding tire size. This information should be in your owner’s manual or sticker on the driver’s door frame or your stock tire’s sidewall—we have explained how to read tire numbers on sidewalls.

Your vehicle tire chart will even come more useful. Here, car manufacturers list different wheel sizes that can fit your car and corresponding tire sizes the rims can take. Online tire calculators can also help you in knowing the best tires for your rim; all you need is to input your rim’s width and offset, already stated in your manual.

With your rim’s information, you can also look for tires yourself but keep in mind that the width and diameter of the tire must match that of your rim. While exceptions might be made for width, it can’t be for diameter. For example, you can go from 225 to 215 or 315, but you can’t go from a 16-inch tire on a 16-inch rim to a 17-inch tire. Going from 225/70R16 to 215/60R16 is possible but not a 215/60R17.

Is it safe to upside tires?

If you know how to upsize correctly, it’s safe. If, however, it is done incorrectly, it may compromise vehicle safety. But first thing first, what are you upsizing? The width, aspect ratio, or overall diameter?  If you’re upsizing the width or aspect ratio (height), don’t go beyond your manufacturer’s recommendations—this is usually stated in your manual.

Too wide or tall tires can cause tires to rub against the wheel housing, brake lines, or even the suspension. It can also alter the accuracy of the odometer, speedometer, steering response, handling, and more.  However, while upsizing can be done on the tire’s width and height, it can’t be done on the diameter so long you’re using the same rim.

An 18-inch rim will only take an 18-inch tire. So if you’re upsizing your tire diameter, you must change your rim size too. And even if you upsize the diameter, don’t go more than 3% higher. For example, suppose your factory tire’s diameter is 24.47; you can only upsize it to 25.20 inches.

Do bigger or smaller wheels make a car faster?

Generally, smaller wheels are lighter and therefore easy to move, hence will make a car faster. Bigger wheels, on the other hand, are heavier, so speed and acceleration will naturally be compromised. 

However, whether smaller or bigger wheels make a car faster depends on your stock wheel. If your vehicle comes stock with a bigger wheel and you downsize a bit, your car will become faster, though stability, handling, and cornering will be compromised.