How to measure your Bicycle Wheel before converting to an E-Bike

a man demonstrating how to measure a bike wheel

When you’re browsing Leeds Bikes for a new electric bike kit, one of the first questions our product pages will ask you is “what is your wheel size?”

example of a Leeds Bikes product page

 

While this may seem like a simple question, it can cause confusion for many people, and with good reason. There are so many different sizes and techniques for measuring that you might not even be sure how to measure a bike wheel. However, the answer is extremely important, since we customize your electric bike wheel to your bike wheel size.

Why Is This so Confusing?

We have many customers who inadvertently order the wrong size, causing paperwork issues and extra shipping charges, which delays the amount of time it will take you to get your e-bike kit installed on your bike so that you can go party!

Part of the confusion is the fact that many people misunderstand what is meant by “wheel size.” The electric bike wheel size is the diameter of the wheel PLUS the width of the tire. For example, a standard 20″ bicycle wheel has an actual diameter of 16.5”, but after you put a 20″ x 1.75″ tire on the wheel, the total diameter actually measures 20”. Confusing, right?

measuring the circumference of a bike wheel

 

If your wheel does not have the size printed right on it, then here are some simple tips on how to measure a bike wheel and ensure you get the RIGHT electric bike wheel.

Step One: Check the Labeling on Your Tire

This is the easiest and most common way to determine the rim size you need. On the sidewall of most commercially-branded tires, you will find a series of numbers that tell you the size of your rim. For example, it might read 26” x 1.5″. This indicates that the wheel is 26″ total, with a 1.5” tire. On a 700c, the numbers on the tire would look more like this:

a close-up of the Rubino PRO Slick bike tire

 

When working with 700c tires, I usually tell my customers not to worry about the first set of numbers at all. The first series of numbers is the “ISO number,” which is basically just a fancier and more complicated way of telling you to look at the second set of numbers.

What you should be looking for is the second line that says “700 x 23c.” But don’t worry if you don’t see any numbers at all. Sometimes the bike tire numbers become worn and unreadable over time. You can still measure the size yourself using the next piece of advice regarding how to measure a bike wheel.

Step Two: Physically Measure the Diameter of Your Wheel

Remember, this is measuring the rim PLUS the bicycle tire. This can be explained in three simple steps:

  1. Hold your tire/rim combination in place. Or, better yet, have a friend hold it for you.
  2. Stretch a measuring tape across the length of the rim AND tire, placing the tape right on top of the axle in order to measure the wheel at its widest point.
  3. Read the number at the far end of your tire. This should be your diameter. You want to measure in inches for every bike size except a 700c, this would be measured in millimeters. A 700c rim should be 622mm, and measured with the tire, should be 700mm.

Step Three: Take it a Step Further and Measure the Circumference

“Well, now why would I want to do that?”, you may ask. It’s true that the circumference won’t tell you what wheel size to choose, but this can be an important measurement for another reason. So, we thought we ought to mention it while showing you how to measure a bike wheel.

If you have purchased one of our bike computers, or you already own some form of bicycle speedometer, odometer, or GPS system, you will want to determine this measurement in order to properly calibrate that device. Just as your car’s speedometer and odometer will provide inaccurate data if you change the size of its wheels, bicycle components must also be set based on the size of your tires. Don’t fret. You still have a few different options on how to find the circumference of your bike wheel.

Option One

This requires some arithmetic. If you have already determined your wheel’s diameter, the circumference can be determined by multiplying that number by pi. Pi is equal to 3.14, so the circumference of a 26” tire is 26 x 3.14, which equals 81.64”. However, if math isn’t your forte, you can try the next option.

Option Two

a close-up of a measuring tape around a bike wheel

Wrap a tape measure or string around the outside edge of your wheel. If you want to measure correctly in order to calibrate your bike computer, then you would want to place the tape measure around the tire. Mark the string or tape measure at the spot where it reaches back to its starting point and measure its length to determine the circumference.

Option Three

Add a dot of wet paint to a spot on your bicycle’s tire tread. Carefully push the bicycle in a straight line for at least two rotations, ensuring the paint marks the ground twice. Measure the ground from the first spot of paint to the next in order to determine the tire’s circumference.

We’re Here to Help!

Choosing an electric bike conversion kit should be a fun and easy experience. Hopefully, by eliminating the stress of learning how to measure a bike wheel, you can focus on bigger decisions, such as what size Lithium-Ion E-Bike Battery is best for you or what other electric bike accessories you might need. As always, we are here to help with any questions you may have. You can email us at leedsbikes@gmail.com 24/7, or call us at (866) 933-8716 Monday-Friday between 9am and 4pm MST.