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How To Measure Bike Tire Size

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If you’re a casual bike rider, chances are, you’re not paying much attention to the size of your bicycle tires. This isn’t good practice, since your bike tire size can really affect your ride.

That said, buying new tires online can be difficult. One of the first questions you’ll be asking yourself is, “what size bike tire do I need?”, and the only way to know is to either look at your bike’s ownership manual, if there’s any or measure your existing tires, especially if the external markings have already worn off.

Even then, if you don’t know how to measure a bike tire, or how to read bike tire sizes, you won’t have much luck figuring what tires you need. Don’t worry, though. Here’s a quick guide that will help you learn how to measure bike tire sizes.

Note: this only applies to adult bike tires. If you want to know how to measure kid’s bike size, click here.

man fixing bike tire

Classification Systems of Bike Tire Sizes

First things first: let us talk about the two common classification systems used for bike tire sizes, so you can understand how to read the tire measurements you’ll get later.

For instance, you might know that your bike tire size is somewhere between 12 to 26 inches, or you think you’ve got 700c tires, but don’t know what that means. This will help you understand that.

Traditional Sizing

The standard system used since bicycles were first invented is the traditional sizing system, which is based on the outside wheel diameter’s measurement. Meaning, the first digits of a bike tire size represents its diameter, then the second ones being the tire width. These units are expressed in inches and are rounded up or down to the nearest inch so you get a full increment.

This classification is not as widely used today due to compatibility issues as bicycle tires and rims evolved throughout the years. Most bike tire manufacturers have opted to use their own sizing structures, which has unfortunately made it more difficult to buy replacement tires.

Standardized Sizing

The International Organization for Standardization (ISO) came up with a more standardized bike tire sizing system that effectively regulated and guided tire measurements as a response to the sizing inconsistencies caused by the arbitrary bike wheel size guides of different tire brands.

The result is a two-digit-dash-three-digit unit that symbolizes the tire’s width and diameter, wherein the diameter refers to the bead diameter, aka where the tire is meant to fit the rim. These tire dimensions are measured in millimeters.

How To Measure Bike Tire Size

As you may have guessed, tire dimensions are all about wheel diameter and tire width. You might also need to know the tire circumference, but we’ll get to that later. In any case, how to determine wheel size on bikes is a pretty straightforward process. You just need a measuring tape and a pen and paper for recording your measurements.

Step 1 : Place the bicycle in an upright position

The first step is to stand your bike on its bike stand or lean it against a wall so you can easily measure the tire size without too much of a hassle. Make sure that the bicycle is standing firmly so it won’t move or tip over.

You may opt to tape the wheel onto the frame so it stays in place while you’re measuring it. Alternatively, you can also have a friend help you out so the next steps will be easier and quicker.

Step 2: Measure the tire diameter

With your measuring tape (preferably a metal one since it’s sturdier than plastic tapes), measure the tire diameter by placing the tape against the tire’s center, then extending it towards the tire’s edge in a straight line. The number you will get is the tire’s radius, so to get the diameter, multiply this number by 2.

If you are measuring to ISO standards, however, measure only to the inner edge of the tire, rather than extending all the way out, then multiply by two.

Step 3: Measure the bike tire width

The next step is to measure the width of the bicycle tire. Place your tape on the ground, lining it across the tire tread in a straight direction. You can record this measurement in inches if you are using the traditional method, or in millimeters, if you’re using ISO standards.

This width is important because it’s indicative of the tire’s intended use. For example, a mountain bike with wider tires is more suited for rough terrain, while road bikes with narrower tires make for smoother and faster rides.

father and son working on bike

Step 4: Combine your measurements

Finally, combine your recorded measurements based on the classification system you want to use. If it’s the traditional system, it should be diameter then width (in inches), and width then diameter (in millimeter) for ISO standards.

These measurements will also give you the tire’s circumference by multiplying the radius by itself, then multiplying it with π. With these measurements, you can look at bike wheel size charts online and figure out which bike tire size you need.

Overview

If you ever needed to find out how to measure bike tire sizes, now you know that it’s a quick and easy process. Just follow the steps listed above, and you’ll be able to have accurate measurements of your bike tires.

The next step is knowing how to take care of your new tires so they last longer and serve you better. That includes learning about road bike tire pressure or using tire pressure detectors. Don’t forget to take care of your other bike parts too, like changing your bike chains. These things don’t just apply to moving bikes, but to stationary exercise and elliptical machines, too.