How to Measure Bike Wheel Size
Many people think measuring bike wheel size is simple, but it’s a bit more complicated. Standard wheel size labels—like 26-inch, 650b/27.5-inch, 29-inch, and 700c—don’t just refer to the rim diameter; they also include the tire thickness. However, due to differences in manufacturing and measurement methods among brands, the actual diameter may vary slightly for tires with the same labeled size once they’re mounted.
Therefore, if you need to buy a compatible replacement tire, knowing how to measure bike wheel size is essential. This guide will teach you two simple methods to measure the diameter and circumference of your bike wheels, helping you find the perfect tire size for your bike.
Basic Concepts of Bike Wheel Size
Before learning how to measure bike wheel size, it’s important to understand the basic concepts. Bike wheel size is typically defined by both diameter and width and is marked using various standards, such as imperial measurements (e.g., 26-inch, 29-inch) and metric measurements (e.g., 650b/27.5-inch, 700c). These markings refer not only to the rim diameter but also to the overall size when the tire is mounted, so tire thickness and differences between manufacturers can affect the total diameter.
Here are some key concepts about bike wheel size:
- Rim Diameter vs. Tire Diameter: The rim diameter refers to the internal metal part of the wheel, while the tire diameter includes both the rim and the mounted tire. Standard wheel size markings typically refer to the tire diameter, such as 26-inch or 29-inch, but the actual size may differ slightly once the tire is mounted. This is because tire thickness and construction vary between brands and models.
- Width: Wheel size is not only about diameter but also includes tire width. The width of the tire affects traction and stability. Wider tires typically provide better grip and cushioning, making them ideal for rough terrain and mountain biking, while narrower tires are better for road cycling, reducing rolling resistance.
- Marking Standards: There are multiple ways to mark bike tire sizes. Road bikes commonly use 700c, while mountain bikes often use 26-inch, 27.5-inch (650b), or 29-inch. The International Organization for Standardization (ISO) has a more precise marking system, expressed in millimeters for rim diameter and width (for example, 622x23mm for a 700c road wheel). This standard helps riders select compatible tires more accurately.
- Size Variations Between Brands: Due to different manufacturing methods, tire sizes can vary slightly between brands. Even if the labeled size is the same, the actual diameter and width of tires from different brands, such as Maxxis or Continental, may differ when mounted on a rim. Therefore, when selecting replacement tires, it’s best to refer to the manufacturer’s specific specifications or measure the tire’s actual size.
- Circumference and Rolling Resistance: For riders who rely on accurate speed and distance data, the wheel circumference (the distance a tire travels in one complete rotation) is another important measurement.
How to Measure Bike Tire Size
Measuring bike wheel size is an essential step to ensure proper tire and frame compatibility. Accurate wheel size measurement can be done by either checking the markings on the tire or manually using a tape measure to measure from the hub to the outer edge of the tire. Additionally, understanding the ISO measurement standard can help you determine tire size more accurately.
Method 1: Reading Tire Markings
Check the tire sidewall: Most bike tires have their size marked directly on the sidewall.
40-622 28×1.50 700×38C :
- ETRTO Standard: 40-622
- 40: Represents a tire width of 40mm, suitable for those seeking more comfort or stronger grip, such as for commuting, hybrid riding, or light off-roading.
- 622: Indicates the tire’s inner diameter of 622mm, which fits the 700C rim, compatible with most road, hybrid, and some city bike rims.
- English Size: 28×1.50
- 28: The outer diameter is 28 inches, compatible with the 700C rim standard.
- 1.50: The tire width is 1.5 inches (approximately 38mm), offering a medium width that provides comfort and stability, ideal for smooth roads or light off-road conditions.
- French Sizes: 700×38C
- 700: Refers to the 700C outer diameter, fitting most road bike rims.
- 38: The tire width is 38mm, suitable for daily riding, city commuting, and light off-road use, offering better grip and comfort.
- C: Indicates that this tire is designed for a 700C rim.
This tire marking indicates that you need a tire for a 700C rim, with a width of approximately 38-40mm. View Bicycle Wheel Size Chart: A Complete Guide.
Method 2: Standard Wheel Measurement
- Measure the diameter: Place one end of the tape measure at the center of the wheel (hub) and measure to the outer edge of the tire. Multiply this number by 2 to get the full tire diameter.
- Measure the tire width: Place the tape measure across the top of the tire to measure the width.
- Put the diameter first and the width second: When purchasing a new tire, remember that traditional sizes list the diameter first, followed by the width. For example, a tire marked 26 x 1.75 has a 26-inch diameter and a 1.75-inch width.
Note: Bike wheel diameters are typically rounded to the nearest half-inch. If your measurement is slightly above or below a standard size, round to the closest value.
Method 3: Using the ISO Method to Measure Bike Tires
The ISO (International Organization for Standardization) method is a more precise way to measure bike tire size compared to traditional inch markings. It provides more detailed and consistent measurements, making it easier to match tires and rims accurately. This method uses millimeters to indicate both the rim diameter and tire width, which helps eliminate variations between brands and tire types. Understanding how to measure bike tires using the ISO method is essential when choosing the right tire, especially when replacing an old one.
1. ISO Standard Marking System
The ISO method uses two numbers to mark tire sizes: the first number represents the rim diameter (in millimeters), and the second number represents the tire width (also in millimeters). For example, a tire marked 700x25C means the rim diameter is 700 millimeters, and the tire width is 25 millimeters. The format for marking is usually: Rim diameter x Tire width.
Here are some examples:
- 700x25C: Rim diameter is 700 millimeters, and tire width is 25 millimeters.
- 26×2.0: Rim diameter is 559 millimeters (ISO standard), tire width is 50 millimeters.
- 650B x 42: Rim diameter is 584 millimeters (ISO standard), and tire width is 42 millimeters.
Note that the ISO standard typically uses millimeters to express the inner diameter of the rim, rather than the traditional inch measurements. For example, a 26-inch tire in traditional sizing is marked as 559mm in the ISO system, and a 700c tire is marked as 622mm.
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2. Measuring Rim Inner Diameter
Use a tape measure to measure from the center of the wheel (hub) to the inner edge of the tire. Multiply this by 2 to get the tire’s diameter, usually in millimeters.
For road wheels, a common rim inner diameter is 622mm (700c), while mountain bike wheels may have rim inner diameters of 559mm (26-inch), 584mm (650B), and others.
Ensure the rim is clean when measuring to get an accurate reading.
Notice: If your tape measure doesn’t have millimeters, measure in inches and multiply by 25.4, as 1 inch = 25.4 mm.)
3. Measuring Tire Width
To measure the tire width using the ISO method, the tire should be mounted on the wheel and inflated to the recommended pressure. Then, use a caliper to measure the widest part of the tire. Keep in mind that the tire’s width may vary slightly due to factors like inflation pressure, materials used, and the tire’s design. Therefore, the actual width might differ slightly from the marked width.
For example, a tire marked 700x25C typically refers to a tire that is 25 millimeters wide when inflated. If you measure and find a slight difference in width, refer to the manufacturer’s specifications to check if the variation is within a normal range.
4. Using ISO Sizes to Select the Right Tire
One of the main advantages of the ISO method is that it eliminates the confusion often caused by inch markings. When purchasing replacement tires, the ISO method helps you match rims and tires more accurately. For example, if your rim is 700C (622mm), you can choose a tire marked with the same 622mm size to ensure compatibility.
Additionally, the ISO system helps you choose the right tire width based on your riding needs. For road cycling, narrower tires (like 700x25C) reduce rolling resistance and increase speed. For mountain biking, wider tires (such as 26×2.0) provide better grip and cushioning.
How to measure bike wheel size （Video）
By watching this instructional video on measuring bicycle wheel size, you can get a more intuitive idea of how to accurately measure wheel size.
Common Wheel Size Terms
- 26-inch: This is the most common wheel size for traditional mountain bikes. With a smaller diameter, it is ideal for technical riding, especially on off-road terrain where agility and control are essential.
- 650b (also known as 27.5-inch): A wheel size between 26-inch and 29-inch, commonly used in mountain bikes and some gravel bikes. 650b wheels offer better rolling performance and traction off-road while maintaining a level of agility.
- 700c: This is the standard wheel diameter for road bikes and some gravel bikes, measuring approximately 622mm in diameter. 700c wheels are designed for higher speed and efficiency, making them ideal for flat roads and long-distance rides.
- 29er (29-inch): While the 29er shares the same diameter as 700c, it usually features wider tires for mountain biking. These wheels roll more easily over obstacles, making them suitable for long-distance off-road riding, offering better-rolling resistance and stability.
Size Guide
| Wheel Size | ||
| ISO length (mm) | Inches (MTB size) | Road Bike size |
| 305 | 16 | |
| 406 | 20 | |
| 507 | 24 | |
| 559 | 26 | 650c |
| 584 | 27.5 | 650b |
| 622 | 29 | 700c |
Road Bike Rim Width and Tire Size Chart
Understanding the correlation between road bike rim width and tire size is essential for optimizing riding performance and comfort. Rim width directly affects tire support and shape, influencing stability and comfort during rides. Below is a concise chart showing the relationship between road bike rim width and tire size.
| Tire Size Compatibility | Internal Rim Width |
|---|---|
| 23 – 25c | 13-15, 17-19mm |
| 25 – 28c | 13-15, 17-19, 20-21, 22-23mm |
| 30 – 33c | 17-19, 20-21, 22-23, 24-25mm |
| 33 – 35c | 17-19, 20-21, 22-23, 24-25mm |
| 38 – 40c | 20-21, 22-23, 24-25mm |
| 40 – 43c | 20-21, 22-23, 24-25mm |
| 43 – 45c | 22-23, 24-25mm |
| 45 – 48c | 22-23, 24-25mm |
| 48 – 50c | 24-25mm |
Mountain Bike Rim Width and Tire Size Chart
Below is a compatibility chart for mountain bike rim width and tire size.
| Tire Size Compatibility | Internal Rim Width |
|---|---|
| 1.9″ Tires | 19-23mm |
| 2.0″ Tires | 19-24mm |
| 2.1″ Tires | 19-28mm |
| 2.2″ Tires | 20-30mm |
| 2.3″ Tires | 21-33mm |
| 2.4″ Tires | 23-34mm |
| 2.5-2.7″ Tires | 25-35mm |
| 2.8-3.1″ (plus) Tires | 22-23, 24-25mm |
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FAQ
Can I change to a different tire size?
Yes, you can switch to a different tire size, but it’s important to ensure compatibility with the rim and frame. It’s advisable to consult a professional to ensure safety when changing tires.
What is the most common road bike wheel size?
The most common road bike wheel size is 700c, which has been the standard for many years. The “700” refers to a wheel diameter of 700 millimeters, while “c” is an old French tire width code. “A” represents the narrowest width, “d” is the widest, and “c” typically refers to a medium-wide size.
Do I need to adjust other components after changing tire size?
After changing the tire size, you may need to adjust the brake system or drivetrain to ensure they fit the new tire size properly.
Conclusion
I hope this article was helpful to you. Although measuring bike wheel size may seem simple, it is crucial for optimizing your bike’s performance. By using the correct methods, you can accurately determine the wheel’s diameter and width, allowing you to select the right tires and components to enhance your cycling experience, whether for daily riding, off-roading, or long-distance touring.
