Adaptiv Sports
 
 

Does Size Matter?

The short answer is; yes of course it does! But in relation to wheelchair wheels why does it matter and what are the differences and benefits to the user of choosing different sizes of rear wheels and front castors. Before we go any further I should explain that we at Adaptiv Sports have come to the world of wheelchairs from the cycle industry and as such are not encumbered by any preconceptions or fixed ideas around what users ‘should’ use or only limiting choice to long established  options; i.e. 22, 24,25 or 26” rear wheels for example. 

Whilst the sizes available to a chair build do have certain limitations; largely based around the dimensions of the user, size and geometry of the chair, the user’s environment, transfer methods and availability of the product. At Adaptiv Sports we always try to work closely with each individual to identify the optimum solution for them; both for their chair’s and adaptive bikes.  Let’s take a closer look at the wheels themselves and what the difference in sizes means to the user.

Rear wheels 

This is an area that can be confusing for the user to navigate. There are a multitude of sizes and widths available. There are broadly three ways of expressing the size of the wheel rim and tyre and these can commonly be viewed on the sidewalls of the tyre as can be seen below: The ‘European Tyre and Rim Technical Organisation (ETRTO)’ metric is expressed in millimeters as the width and inner diameter of the tyre. The ‘Inch’ metric is expressed in inches as the outer diameter of the tyre and the overall width. Just to add another level of confusion the third metric is the ‘French’ one and this is expressed in millimeters as the approximate outer diameter of the tyre followed by its width – rest assured we will help you to choose the right size for you!

There are various online resources to convert tyre sizes. I have included one example which just covers the 25/26” options to give you an idea of what is available! 

Wheelchairs have traditionally been supplied with 24, 25 or 26” wheels and narrow 1” tyres. With the market forces of demand and supply manufacturers then mass produce tyres around these sizes and choice outside of these sizes becomes limited. This has manifested itself in the cycle industry with the popularity of larger mountain bike (MTB) wheels such as 27.5 and 29” resulting in reduced production and availability in sizes that have fallen out of fashion such as the 26” wheel and tyre.

Whilst the traditional 24, 25 or 26 x 1” wheels and tyres, inflated to high pressures (100 PSI and above) have their advantages in terms of speed and reduced rolling resistance. Larger wheels have the benefit of  easier rolling over obstacles and undulations and provide a ‘smoother’ ride. Coupled with a larger, wider or higher volume tyre which can then be run with less inflation also provides a more comfortable ride with a larger contact patch and improved grip. This also opens up the possibility of tyres with different tread patterns or features like tan sidewalls.

For a chair user, the taller individual with a longer trunk and arm length would generally benefit from a larger rear wheel and tyre. However this can have an effect on the seat to floor height of the chair and this again needs to be considered when assessing how the individual propels their chair and any environmental limitations. 

When we suggest a rear wheel size it is often one that has been carefully selected to work the best for you and your chair in the environments in which you use it. It would be impossible to do this without careful and considered assessment. Once the wheel size has been selected the chair geometry is built around it. At the heart of Adaptiv Sports are two active chair users with a combined experience of 35 years and this experience has been harnessed, informing our assessment, prescription and procurement processes.

Front castors

Equally important is the size of the front castor wheels. Why is this? Well it’s the first thing that your chair makes contact with as you propel it forwards (or drive it forwards more quickly in the case of adding a power assist device to your chair). Castors are like the three bears porridge; too small and they’ll catch on objects or undulations and spill you forwards in the chair, too big and they’ll have a negative impact on the maneuverability of your chair as they move through the arc of their rotation as your chair is moved around. So a ‘just right’ solution is required!

It’s therefore important to get the right size for you and your requirements. Castors on active chairs are usually offered in 3,4 or 5”. The smaller the castor, the quicker and more ‘agile’ the front of the chair feels. However, back in 2017 I was in training for the London Marathon (I had entered to complete it in my everyday chair). Whilst out on 20 mile training pushes I changed my front castors to 5” from 4” and couldn’t believe what a positive effect this had on the ride quality of my chair and how it rolled more efficiently over uneven terrain. As with the rear wheels a slightly wider ‘soft roll’ castor tyre will provide for a smoother and more comfortable up front.

Please do get in contact for any advice on wheel and castor size. We are always happy to help!