Wheelchair tyres are often marked with both traditional imperial and ISO metric sizing. For example, a tyre may be labelled 24 x 1 3/8 (37-540).

While 24 x 1 3/8 is a commonly used traditional tyre size, the ISO measurement in brackets – 37-540 – is the most important number to look for when choosing a replacement tyre. The ISO measurement is more precise because it identifies the tyre width and, most importantly, the bead seat diameter of the rim in millimetres.

What Does 37-540 Mean?

The ISO size 37-540 consists of two measurements:

• 37: The nominal width of the tyre in millimetres.
• 540: The bead seat diameter (BSD) of the rim in millimetres.

Why Is the ISO Size Important?

The 540mm bead seat diameter is particularly important when replacing a wheelchair tyre. It identifies the diameter of the rim where the tyre bead sits.

The tyre must have the correct bead seat diameter to fit the rim properly. This is why the ISO measurement is more reliable than simply matching the traditional imperial size.

If your existing tyre is marked 24 x 1 3/8 (37-540), use 37-540 when searching for a replacement. The imperial size is useful as a general reference, but the ISO measurement provides the more precise specification.

How to Find Your Wheelchair Tyre Size

The tyre size is normally printed or moulded into the sidewall of the tyre. Look for a number containing a hyphen, such as:

37-540

You may also see the ISO size alongside an imperial measurement, such as 24 x 1 3/8.

If both measurements are shown, pay particular attention to the ISO number in brackets. This is the measurement to use when checking compatibility with a replacement tyre.

37-540 Wheelchair Tyres

SWC supplies a range of wheelchair tyres and inner tubes, including tyres with an ISO size of 37-540.

For example, our 37-540 wheelchair tyre is available for standard pneumatic applications. If you want to eliminate the risk of punctures, we also supply a 37-540 puncture-proof wheelchair tyre.

If you are using a pneumatic tyre, you may also need a replacement 37-540 inner tube.

Need Help Finding the Right Wheelchair Tyre?

If you're unsure which wheelchair tyre you need, check the markings on the sidewall of your existing tyre and look for the ISO measurement. A photograph of the tyre sidewall can also help identify the correct replacement.

Browse the full range of wheelchair tyres and inner tubes at SWC, or contact us if you need help finding the right size.