What do the numbers on a tire mean?

By: Sr vini

Do you know about your car tire’s dimensions? Probably not, if you are not much of a car enthusiast. But you surely have seen some numbers imprinted on the tire sides. Actually, these numbers have a lot of information about the tires. This includes information about tire width, tire type, aspect ratio, diameter, construction, etc. So let’s get to know exactly what do the numbers on a tire mean? 

What do the numbers on a tire mean?

There are a lot of numbers and letters imprinted on the side of the tire, like, P225/45R17 91V. All these numbers have a whole lot of information about tires. So we have a breakdown of that information for you so that you can easily know about your vehicle’s tire!

What do the numbers on a tire mean

1) Tire Type (P, LT, ST) 

The majority of tire sizes begin with one or more letters, such as P or LT. The letters are sometimes embedded on the last of the code. The Letter indicates the vehicle or service for which the tire was intended.

The letter “P” preceding the “Tire Size” indicates that the tire is a P-Metric tire designed for passenger automobiles. If you have a car, you will surely see this Letter. 

If a tire size does not begin with a letter, it is a Euro metric tire. The load capabilities of P-Metric and Euro-Metric tires may vary.

The initials “LT” at the start or end of the tire size denote that the tire was built for light vehicles. These are frequently fitted on 3/4 tonne and 1-tonne trucks and SUVs.

“ST” is an abbreviation for Special Trailer. Travel trailers, fifth wheels, boat trailers, and utility trailers are all equipped with these tire types and have “ST” embedded as code. 

2) Tire Width (3 Digits) 

The tire’s width is measured in millimeters by the three-digit number after the Letter. For example, your car has P235/55R18 this code. 

The grouping “235” denotes the tire’s width from sidewall to sidewall in millimeters. Thus, the tire is 235 millimeters — 9.25 inches — broad from sidewall to sidewall in this case.

3) Aspect ratio (Two digits after the slash) 

The Aspect Ratio measures the tire’s cross-sectional height to width as a percentage. Having a larger aspect ratio means that a tire’s sidewall will be taller. Tire sidewalls display the aspect ratio as a percentage. If you measure from the wheel rim to the top of the tread, this is the height of the sidewall. It’s a percentage of the width of the tire.

As an example, your car’s tire has the P235/55R18 designation. The aspect ratio, in this case, is 55, which means that the sidewall is 55 percent as tall as the tire is wide. To get the sidewall height, convert the 235 mm tire width to inches (9.25). Then multiply by 55%. (.55). This results in a value of 5.2, which is the sidewall height in inches.

4) Construction (Single Letter) 

Then comes the single Letter, which is often “R” or sometimes “D.” This single Letter provides information about the tire’s internal structure.

The “R” indicates that the layers run perpendicular to the tire’s circumference. Today, the vast majority of tires on the road are radial tires, which have internal layers that are perpendicular to the rotation axis (and the direction of travel).

Bias-constructed tires are identified by the letter “D,” which refers to the use of diagonal (crisscrossed) plies in their construction. They are also called conventional, x-ply, or cross-ply tires in some places. There are still a lot of motorcycle and trailer tires that have this type of construction inside them.

5) Wheel Diameter (Two Digits) 

This two-digit number tells you how big the wheel is in inches. How far apart are the two bead seats? This is a very important number. This is the number you’ll use to figure out your tire size. 

Like, we have taken the P235/55R18 tire number example. The “18” number tells you that this tire would fit a rim with an 18-inch diameter.

6) Load Index (Two or Three Digits) 

You may also see two digits and one Letter after the main code. Load Index tells you how much weight the tire can hold when it’s properly inflated. In terms of tire capacity, the higher number you see, the more capable the tire is at bearing weight.

For example, your tire number is P225/ R 18 94Y. In this case, 94 is the load index. It means the tire can bear a maximum weight of 1477 lbs. You can easily find the load index on the web. 

7) Speed Rating

Then comes the last digit, which represents speed rating. This is the maximum speed at which a vehicle may be operated safely for an extended period of time. A tire with a greater speed rating is better able to withstand heat and maintain control at higher speeds.

Like in tire number P225/ R 18 94Y, Y is the speed rating. According to the speed rating index, a tire with a Y rating can go to the highest speed of 186 mph. 

What do the three numbers on a tire mean?

The first three digits in the tire represent tire width. These three number comes after one Letter, majorly “P.” Section width may also be used to describe this term.

For instance, your vehicle’s one tire has the P235/55R18 code. The designation “235” refers to the width of the tire from sidewall to sidewall in centimeters. Thus, the tire is 235 millimeters — 9.25 inches — wide from sidewall to sidewall in this situation.

What is the aspect ratio of a tire?

The Aspect Ratio is a percentage value that indicates the tire’s cross-sectional height to width ratio. A greater aspect ratio results in a higher sidewall on a tire. On the sidewalls of tires, the aspect ratio is shown as a percentage. 

For instance, your car’s tires are designated P235/55R18. In this situation, the aspect ratio is 55, indicating that the sidewall is 55% tall as the tire. To get the sidewall height, convert the 235 mm tire width to inches (9.25) and then multiply that number by 55. The resulting sidewall height will be 5.2 inches, which is the tire’s aspect ratio.

What do the numbers on a motorcycle tire mean?

Motorcycle tire has different numbers than the car or any other vehicle. The motorcycle has codes like 160/70 B 17. So what do these numbers mean? Let’s find out!

1) Width of Tire (Three digits)

The millimeter width of your tire is indicated by the first three numbers on your motorbike tire. A straight line through the tire is used to measure its width. You may see it from one side to the other while you ride a motorcycle.

2) Aspect Ratio (Two Digits)

The second two digits indicate the aspect ratio of your motorbike tires. It’s a measurement of the tire’s height in relation to its width that’s used to calculate the aspect ratio. Tire width and tire height are used to calculate this aspect ratio, which has a decimal point at the end of the percentage.

3) Internal Construction (Letter)

You can identify if a tire is Bias Ply or Radial by the Letter between the second and third digits, R or B, respectively. The tire is classified as Bias Ply if it lacks a letter.

4) Rim Size (Two digits)

The third digit on your tires represents your wheel’s rim size, or circumference. Therefore, if the number is 18, it indicates that your tire rim is 18 inches in diameter. A tire with the third number of 16 indicates a rim size of 16, and so forth.

5) Alphanumeric code

Some bike tires have a code like M/C 62 H, after the main ture code. MC stands for motorcycle, and 62 is the load rating index or the load-bearing capacity the tire can handle at full inflated. H is the speed classification of the tire, with an H-rated tire being safe at sustained speeds of up to 130 mph.

Bottom Line

Now you exactly know what do the numbers on a tire means. You can easily figure out your vehicle’s tire specifications. Moreover, it will become easy for you to explain when getting your tire replaced or any Repairs.

We hope this article was helpful & informative. Leave your valuable thoughts & suggestions in the comments!