We can measure a tire’s diameter by measuring from the outer edge of one bead (or rim) to another. While we’ve come across some tires that were much smaller or larger than their advertised diameters, most tires are within about 2 percent of the advertised diameter.
The easiest way to find your tire’s measurements is to check the sidewall of the tire, which you can do without taking the tire off. To find the diameter of your tire, look for a capitalized “R” followed by a number, such as R15.
Another measurement you’ll see on a sidewall is the aspect ratio. This is usually represented as a percentage and determines how tall or short a tire is.
Table of Contents
How to measure tire size
The “R” stands for “radius,” and that number indicates how far across the tire is from one side to the other. The diameter is twice this distance, so that same R15 tire would have a diameter of 30 inches.
Find out what your rim size is. If you don’t know what size wheels your car uses, you can find out by looking in your owner’s manual or by measuring it yourself. The rim size is a measurement of how wide in inches it is from one end to the other.
Know what type of tires you have on your car now. Tires come in two types: bias ply and radial. Bias-ply tires are older but still available for use on some cars; radial tires are more common today and feature a layer of cords running at 90-degree angles to each other from side to side.
The number after “R” indicates the diameter in inches, so an R15 has a 15-inch diameter.
The next number is the width of your rim in inches, so if your tire says “16X7,” it means that your wheel is 16 inches in diameter and 7 inches wide.
If you don’t see any numbers on your tire or if you want to double-check them, follow these steps:
– Measure from one side of the rim to the other side (see image above).
– The measurement should be taken on a flat surface and with a standard metal tape measure.
– Use this measurement to calculate the circumference of your wheel by multiplying it by 3.14 (pi).
This would give you the distance around the outside of the wheel (in inches) if you were to take a string and wrap it all the way around.
How do you measure tire size in inches?
All tires have a “tire size” printed on their sidewall, which contains all of the information you need to know about that specific tire, including its dimensions. For example, the most common passenger tire size is P215/65R15.
Each letter and number in this sequence provides important information about the tire’s measurements and capabilities.
Tire size is the measurement of a tire from one sidewall to the other, which is expressed in millimeters for metric tires and inches for standard tires.
For instance, if your tire reads 25×8-12, the diameter of your wheel is 12 inches.
You can tell the size of a tire by looking at the numbers on the side of the tire. For example, 265/65R18. The first number is called the width, or cross-section width. It’s the widest point from sidewall to sidewall in millimeters.
The second number is called the aspect ratio, or profile height. It tells you what percentage of the tire’s width is its height. In this case, 65 means that this tire’s sidewall height (from rim to tread) is 65 percent of its width.
This percentage is also referred to as the series of the tire. A common misconception is that “R” stands for radial, but it actually stands for “rim diameter.” So, in this case, R18 means that this tire fits an 18-inch wheel rim.
What does the 265 70R17 mean?
The type of tire you need depends on your vehicle, driving habits, and regional weather conditions. While our comprehensive tire guides can help you select the correct tire for your vehicle and climate, you may still be wondering how to decipher the meaning behind the numbers and letters in each tire size.
First, let’s start with the basics. Tire size consists of three sets of numbers and letters that correspond to a specific measurement of your tire.
These measurements are known as metric sizing, and your tire size is printed directly on your tires sidewall. The meaning behind each number in a metric sized tire is as follows:
265 = This is the width of the tread in millimeters, measured from one side of the tread to another.
70 = This two-digit number represents the aspect ratio or profile height which is represented as a percentage of the tires section width.
R = R is an indicator of construction used exclusively for radial tires. Bias-ply tires will have no letter at this position of their tire size marking.
17 = The diameter of the wheel that this tire fits measured in inches from one end to the other through its center point.
Can I use 60 instead of 55 tires?
You should not use 60 instead of 55 tires. The difference in size is too big, and your car will not fit those tires.
The only exception could be if you have aftermarket rims that have a big enough offset that these tires can fit in the wheel well. However, this is not recommended if you don’t know exactly what you are doing.
A safe bet is to buy the same size tires as your car came with from the factory.
What do the three numbers mean on tire size?
The first three-digit number in the tire size refers to the tire width. For instance, in size P215/65 R15 tire, the width is 215 millimeters.
Another example would be a 265/70R17 tire. It has a sidewall height of 70% of its width or 265 millimeters x .70 = 184 mm (7.25 inches).
The last two digits refer to the diameter of the wheel rim that the tire fits onto. In this case, it’s 15 inches. The letter P at the beginning of the tire size means a Passenger Vehicle tire. R stands for Radial construction, and 16 is for the rim diameter in inches.
How to read tire size in inches?
A tire diameter calculator is a tool that can help you determine your tire diameter. This will come in handy if you need to purchase new tires and need to know what size you should purchase.
When it comes to tires, there are many different sizes and types of tires, so it is important to know what size you need before making a purchase.
The first thing you will do when using the tire diameter calculator is measures the circumference of your tire. The circumference is the distance around the tread of the tire.
The easiest way to measure the circumference of a tire is to take a piece of string and wrap it around the tread.
If you have measured correctly, then you will find that the string will make a perfect circle around the tread of your tire.
Once you have measured this distance, all you have to do is divide it by 3.14 (the equivalent of pi), and you will have your tire’s circumference.
Why use our tire diameter calculators?
The size of a tire’s tread determines how much contact it has with the road. Wider tires have more traction and more stability, but they weigh more, take longer to accelerate, and take longer to stop.
The most important reason is that different manufacturers use different tire construction methods, which affect the overall diameter of their tires.
So if you’re looking for an exact fit for your vehicle, you’ll need to know what the difference in diameters will be. Our calculators can help by telling you the diameter of a given tire and how much bigger or smaller it is than the original tire.
In addition to our base calculator, we offer two other calculators. The first is a speedometer/odometer correction calculator. This will tell you how much your odometer and speedometer reading will change with the new tire size.
The second calculator is a gear ratio calculator. This will tell you how much your transmission gear ratio changes with the new tire size.
This information is especially important if you are tuning your car for better performance or if you want to replace your tires with the ones from another car, but keep your odometer and speedometer readings accurate.
What does the size of a tire tread mean?
The tire tread is the surface that contacts the road. The depth of the tread on a tire is important for many reasons, and one of them is safety.
It affects how quickly your car will stop in wet weather. The deeper the tread on your tire, the longer it takes for water between the tread grooves to be cleared from the road surface. This means that there is better contact with the road, which improves handling and braking.
Tire treads can also affect how well your car will drive when it’s icy outside. The more grip your tires have on ice and snow, the better you’ll be able to control your vehicle in winter conditions.
Lastly, if you’re looking for a good all-around performer for most driving conditions, a set of tires with an all-season design should be sufficient.
These tires are designed to handle a variety of conditions, but they aren’t recommended for severe winter weather or heavy off-roading.
Frequently Asked Questions
1. How do you measure tire sidewall size?
The sidewall height is usually specified in mm or %. Sidewalls with a number value (e.g., 55) are specified in mm, and sidewalls with a percentage (e.g., 55%) are specified as a percentage of the tire width.
For example, if your tire has a sidewall height of 55% and a width of 225 mm, then you can calculate the sidewall height using this formula:
55% x 225mm = 123.75mm
2. What size tire is a 265?
The first three digits (265 in our example) refer to the width of the tread in millimeters measured from sidewall to sidewall. The second two digits (45 in our example) refer to the height of the sidewall as a percentage of the tread width.
3. What does the 113s mean on tires?
113s means the load rating of the tire. The higher the number, the higher the load rating.
4. Can I use 235 tires instead of 225?
Yes, you could. The nominal diameter of the 225/75-16 is 29.5 inches. The nominal diameter of the 235/85-16 is 30.7 inches. The 235/85-16 is 1.2 inches larger in diameter than the 225/75-16.
5. What is P265?
A P265/75R15 tire, for instance, indicates a tire that has a section width (distance from sidewall to sidewall) of 265 millimeters and an aspect ratio (sidewall height compared to width) of 75 percent when mounted on a wheel that has a 15-inch diameter.
Conclusion
The sidewall of a tire contains many important details about the tire, and these details are what you need to find the right replacement. To determine your tire size, start by locating your rim size in inches.
This will be a number like 15, 16, 17, or 18. Next, look at the second number on your tire’s sidewall, which is the width of the tire in millimeters.
Afterward, look for the two-digit number after the slash mark. This final number is the aspect ratio or tire profile.
Examine all three numbers together to determine whether you have a standard, low profile, or extra-deep tread tire.
