Understanding Wheelchair Tyre Sizes (ETRTO Guide)
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If you’ve ever searched for wheelchair tyres, you’ve probably seen sizes referred to as 24”, 25” or 26” wheels. The problem is that these terms can often be confusing and inconsistent, as there are multiple tyre and rim combinations that fall under those descriptions.
The most accurate and reliable way to identify wheelchair tyre sizes is by using the ETRTO sizing system.
What Is ETRTO?
ETRTO stands for the European Tyre and Rim Technical Organisation. This system uses metric sizing in millimetres and removes the confusion that often comes with traditional inch-based sizing.
An ETRTO size will usually appear on the sidewall of the tyre in a format such as:
- 25-540
- 37-540
- 25-559
- 54-507
- 25-590
The first number refers to the approximate tyre width in millimetres.
The second number refers to the rim diameter (also known as the bead seat diameter) in millimetres. This is the critical measurement that determines compatibility between the tyre and wheel.
The Most Important Rule
The tyre and rim diameter must always match.
For example:
- A 540 tyre only fits a 540 rim
- A 559 tyre only fits a 559 rim
Tyres and rims must always share the same ETRTO diameter. A 559 tyre will not fit on a 540 wheel.
This is why relying purely on inch sizing often causes confusion.
Common Wheelchair Tyre Sizes
| Nominal Size | ETRTO Size | Typical Application |
|---|---|---|
| 22 × 1 | 25-489 | Common 22" wheelchair wheels |
| 22 × 1 | 25-501 | 22" wheelchair wheels with slightly larger rim diameter |
| 24 × 1 | 25-540 | Standard 24" wheelchair wheels |
| 24 × 1 3/8 | 37-540 | Wider 24" wheelchair tyres |
| 24 × 1.75 / 24 x 2.0 | 47-507 / 50-507 | Typical off-road wheelchair wheel tyre sizes |
| 25 × 1 | 25-559 | 25" wheelchair wheels |
| 26 × 1 | 25-590 | 26" wheelchair wheels |
Different Tyre Widths on the Same Rim
One important thing to understand is that multiple tyre widths can fit the same rim diameter.
For example, all of the following tyres fit a 540 rim:
- 25-540
- 28-540
- 37-540
The width changes, but the rim diameter remains the same. You can install a variety of different width tyres on the same rim to suit different needs or preferences.
Where To Find Your Tyre Size
The ETRTO size is usually stamped into the sidewall of the tyre.
Sometimes it can be difficult to spot because:
- it may be moulded into the rubber
- it can be hidden within the tread pattern
- the text may be very small
If unsure, it is always best to check the markings directly on the tyre before ordering replacements.
Understanding Overall Wheel Diameter
The second ETRTO number (such as 540 or 507) refers to the rim diameter in millimetres, not the total outside diameter of the wheel.
The overall rolling diameter of a wheelchair wheel depends on:
- the rim diameter
- the tyre width and profile
This is why a lot of 507 off-road wheel setups are compatible with standard 24" (540) wheelchair setups. Although the rim itself is smaller, the larger tyre profile increases the overall wheel diameter.
For example, a 47-507 off-road tyre setup maintains an overall rolling diameter relatively close to many standard 24" wheelchair wheel setups, while larger 50-507 or 54-507 tyres can bring the overall diameter closer to some 25" (559) wheel configurations.
Need Help Choosing the Correct Tyre?
If you’re unsure about your wheelchair tyre size, the safest option is to check the ETRTO marking printed on your current tyre and provide that exact size when ordering.
That removes guesswork and helps ensure the correct tyre is supplied for your wheelchair.