A Simple Guide: Understanding Wheelchair Tire Sizes

Decoding the Numbers

Understanding wheelchair tire measurements can be surprisingly complex, especially when navigating between wheelchair and bicycle tire specifications. This comprehensive guide will help you make sense of the numbers and ensure you get the right tire for your wheelchair every time.

1. The Wheelchair-Bicycle Tire Connection

One of the most important things to understand about wheelchair tires is that they're not manufactured by wheelchair companies - they're made by bicycle manufacturers. This creates an interesting challenge because bicycle and wheelchair measurements don't always align perfectly.

Example of a wheelchair tires on a bike website that we would call a 25" and is shown with as a 26" tire.

2. Understanding Measurement Systems

There are two primary measurement systems:

Imperial (Traditional) Measurements in Inches:

24" x 1"
25" x 1"
26" x 1"

Metric Measurements (More Accurate) in Millimeters:

This measurement is also referred to as the International Organization for Standardization measurement or ISO measurement.

25-540 (equivalent to 24" x 1")
25-559 (equivalent to 25" x 1")
25-590 (equivalent to 26" x 1")

Common Size Conversion Chart:

Imperial Size	Metric Size	Actual Rim Diameter
22" x 1"	25-504	504mm
24" x 1" BMX Tire (as a comparison)	25-507	507mm
24" x 1"	25-540	540mm
25" x 1"	25-559	559mm
26" x 1"	25-590	590mm

3. Common Tire Sizes and Their True Measurements

The metric measurement system uses two numbers:

First number (e.g., 25): Represents tire width in millimeters
Second number (e.g., 540): Represents the internal rim diameter in millimeters

For example:

25-540: 25mm wide tire, 540mm rim diameter (1" tire on a 24" wheelchair wheel)
35-559: 35mm wide tire, 559mm rim diameter (1-3/8" tire on a 25" wheelchair wheel)

4. How to Choose the Right Tire

Pro Tip: Always ignore imperial measurements and focus on the metric numbers.

Here's why:

More precise
Universal standard
Eliminates confusion between wheelchair and bicycle sizes
Ensures a correct fit every time

When shopping for tires:

Check your current tire's metric size
Look for the corresponding metric measurement
Match both the width (first number) and diameter (second number)

5. Shopping Tips

When visiting a bicycle shop:

✓ DO specify the metric size (e.g., "I need a 25-540 tire")

✗ DON'T just ask for a "24-inch tire"

Common Tire Width Options:

18mm = approximately 3/4 inch
25mm = approximately 1 inch
28mm = approximately 1 1/8 inches
35mm = approximately 1 3/8 inches

Important Note: Post-COVID, many tire manufacturers have updated their labeling, which can cause confusion. Some tires labeled as "26 x 1" might actually be different sizes. Always verify the metric measurements (559 vs 590) to ensure proper fit.

Conclusion

Understanding wheelchair tire measurements doesn't have to be complicated. By focusing on metric measurements and knowing your specific size requirements, you can avoid common purchasing mistakes and ensure you get the right tire every time.

Remember:

Always use metric measurements when possible
Verify both width and diameter numbers
Don't rely solely on imperial measurements
When in doubt, check the metric size on your current tire

This guide should help you navigate the sometimes confusing world of wheelchair tire measurements with confidence. Whether you're replacing tires yourself or working with a bicycle shop, you now have the knowledge to ensure you get the correct size every time.