What is the most common wheelchair tire size?

Functionally rear wheels are critical components in manual wheelchair configuration and performance. They are two of the four points of the wheelchair that come in contact with the environment (along with front casters) and they are the instrument through which independent manual mobility happens! If you look at the complete configuration, rear wheels consist of three components: the wheel itself, the tire and the handrim. Here we will dive deeper into the variety of specific wheel properties and how they can impact performance for the user.

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Size

The size of a rear wheel can have an effect on performance for many reasons. Size can dictate rear seat to floor height; the larger the wheel the higher the potential rear seat to floor height, depending on where it is placed with respect to the wheelchair frame.  This can be important to ensure proper access to one&#;s environment and should be considered when working with very tall clients. 

This height and size can also impact the users&#; access to the wheels and upper extremity position during propulsion. Remember, that ideally, we want elbow flexion of 60-80 degrees when the users hand it at the top of the handrim for the most efficient propulsion stroke. The size and position of the rear wheel will impact this.

Generally, a larger wheel can increase propulsion efficiency as it allows longer contact with the rim during the active phase of a propulsion stroke and well as a larger area of contact are with the ground for traction. A larger wheel diameter will effectively roll farther with each push, minimizing the number of pushes per day.  Size can also have an influence on maneuverability within the environment, a larger diameter rear wheel makes maneuvering on rougher terrain easier due to its enhanced ability to climb objects but, depending on its position within the wheelchair frame, can make the wheelchair footprint slightly larger making it difficult to navigate very tight spaces, but with proper set-up this could be avoided. Typical rear wheel sizes for a manual wheelchair will range from 20&#;-26&#; in diameter, 24&#; being the most common.  You should consider both accessibility and propulsion efficiency when selecting the appropriate size.

Weight

Just like all components for manual wheelchairs, weight can be a significant factor when considering rear wheels. During independent propulsion the rear wheel is the component which is manipulated to move. Due to physics principles, such as inertia, an object that is heavier will take more effort to start moving and to stop when it is in motion.  Research tells us that 63% of the manual wheelchair users movement patterns are typically short and slow bouts of movement. The majority of these bouts are shorter than 30 seconds, shorter than 13 meters and slower than 0.5 meters per second. This tells us that manual wheelchair users, similar to people who are ambulatory, start and stop a lot. The lighter the rear wheel, the less force it will take to start and stop the wheel, which can have a positive impact on the upper extremities and improve energy expenditure throughout the day.

The weight of a rear wheel can vary based on design, materials and size. However, when considering weight of a rear wheels we also need to consider the weight of the tire and the handrim we add to the wheel, as these components can also vary in weight. Remembering that it all adds up will help us make conscious decisions with our clients for the best balance between weight and performance.

Design

When looking at the design aspect of a rear wheel we want to select features that are going to provide the performance we want for an individual user. Specifically, we look for the stiffness of a wheel when determining efficiency. Flex within a wheel will decrease efficiency as the energy from propulsion is being lost in the unwanted movement of the wheel. Ideally there is high energy transfer from propulsion to the wheel, this will decrease propulsion rate preserving upper extremities.

The two most common categories of rear wheels are mags wheels and spoked wheels.

Mag Wheels

Mag wheels are usually molded of various composite materials. While often a common selection for lower-end manual wheelchairs they tend have more flex within the structure, therefore increasing the energy needed to propel the wheelchair. Also, due to their design mag wheels can warp overtime and this cannot be fixed. Mag wheels are also significantly heavier than spoked wheels and can add up to two lbs (1 kg) per pair as compared to a standard spoke wheel.

More recently, there are higher-performance mag wheels on the market which are composed of lighter and stronger materials to negate some of the negative effects of a traditional mag but even still they tend to be heavier and less efficient than a spoke wheel. The benefit for some users of a mag wheel, is the lack of maintenance required.  However, we do have to remember that since Mag wheels have tendency to warp, they do need to be examined and replaced over time.

Spoke Wheels

Consisting of a rim, spokes and hub a spoke wheel is the gold-standard for independent propulsion. Due to their design, they are lighter and have less flex, increasing propulsion efficiency for the user. Within this category of rear wheels there are many options to be considered. Each of these options can influence the weight, durability and efficiency.

Rims: Wheel rims can be composed of a variety of materials such as steel, aluminum alloys or performance materials such as titanium, magnesium or carbon fiber. Each material has a different balance between weight, durability and other properties such as vibration damping. These higher-end materials allow for an increased stiffness to weight ratio and added strength. Wheel rims are categorized in terms of single, double and or even triple wall.  This refers to the number of layers the rim is composed of and can impact strength.

Spokes:  The number of spokes and the material can impact stiffness and durability. Durability is also determined by the way a spoke attaches to the rim at the hub(center) of the wheel. All spokes should be at the same tension, being &#;true&#;, to allow the wheel to roll straight and efficient.

• Materials: Spokes come in a variety of materials including steel, aluminum, carbon fibre, titanium and fibers such as Spinergy&#;s patented PBO&#; Spoke. All materials come with their ratios of weight and durability but also esthetic and design, some even allow colour choices.
• Quantity: The more spokes the wheel has the less the load is across the hub, spokes and rims which typically improves strength and stiffness. Increasing the number of spokes on the wheel is one way to increase durability and reliability but can come with a weight disadvantage. However, fewer spokes can impact wheel stiffness.
• Attachment: Spokes attach to the wheel with a special nut called a nipple. Nipples allow adjustment in spoke tension which is how you can &#;true&#; a wheel. Spokes have two ways of attaching to the hub of the wheel, J-bend or straight pull.

J-bend spokes are the more traditional option, with a 90-degree bend at the hub which looks like the letter 'J&#;, whereas straight pull spokes have no bend. Straight pull spokes are more durable as they can have a higher tension; the bend in the J style can be a weak point.

There is a perception that spoke wheels require a lot of maintenance, but it really dependent on how the chair is being used. For example, a user who is often on rough terrain, frequently jumping off elevations or extreme lateral movements may be required to tune their spokes more often to ensure the wheel is true. For a typical active user, maintenance of spoke wheels would not be an issue, especially when compared to the trade-off of increased efficiency and performance.

Cost

When it comes to cost of a rear wheel there is a large price range. Typically, a manual wheelchair will have a standard no-cost option available, that may have few performance features and may be offered in limited sizing options. Most manual wheelchair manufacturers will offer a variety of options for rear wheel upgrades including ultralight wheels, such as the Motion Composites Newton Gravity wheels, or wheels from after-market companies such as the popular Spinergy wheels. These upgraded wheels offer more performance characteristics but can also cost more. For example, the Newton Gravity from Motion Composites, a light weight, high-strength, aluminum rim with stainless steel spokes is approximately $350, and the Spingery Blade, with carbon fiber rim and bladed PBO fiber spokes costs approximately $.  Despite added costs rear wheels are a feature that can have an impact on propulsion and efficiency and performance and should be considered carefully for all users.

Due to the wide variety of properties which can make up a rear wheel it is easy to understand how there are numerous options to choose from. Whether it is the wheelchair manufacturers standard wheel or an after-market wheel, matching the features to the users&#; goals will help us ensure we have a good match to maximize performance.

References

1. Sonenblum, S., Sprigle, S., & Lopez, R. (). Manual Wheelchair Use: Bouts of Mobility in Everyday Life. Rehabilitation Research and Practice, , &#;. https://doi.org/10.//
2. https://www.cyclingabout.com/the-best-rims-for-bicycle-touring/)
3. https://www.bikeexchange.com.au/blog/mountain-bike-wheels-what-to-know

Kirk Williams is a photographer, filmmaker, athlete, travel junkie, entrepreneur and public speaker. In the 12 years since he sustained a C6-7 SCI, he has ventured all over North and South America in his custom-built Campervan. He is the founder of Impact Overland, a travel blog that is raising funds to help supply wheelchairs to those in need. Follow him and see his work on Instagram @kirkscamera and
@impact.overland.

I am often asked why I use knobby tires on my wheelchair. Since most manual chair users roll on a skinnier tire, my knobbies stand out. It&#;s a style thing, sure, but they&#;re not just for style points. &#;I spend a lot of time off the pavement, and the knobbies are easier to use on that type of terrain,&#; I usually answer.

Wheelchair users also sometimes ask where they can get a set, but that question requires a much more involved answer. Wheel size, chair geometry and rolling resistance are just a few things to consider when selecting tires, and the simple act of putting wider tires on your chair can have a big impact on its fit and performance.

My attempts to fully answer that question have become something bigger &#; a guide to everything you didn&#;t know you needed to know about selecting the right wheelchair tires for your life. I hope that after reading this, you will be able to better understand the nuances of the various options for wheelchair tires and make an informed decision about which setup best suits your needs.

Rim-Tire Size Hack for Summer/Winter Street/Off-Road

My activities tend to waver from urban wheeling to off-road, and living in California I frequently go from the temperate foothills to the snowy Sierra mountains. In my quest for maximum efficiency, I strive to always have the right tires on my chair.

I use 1-inch high-pressure for urban wheeling and 2.1-inch knobby tires for off-road or snowy conditions. The problem is, I use the same rim for both, and the diameter of a 2.1-inch knobby tire is significantly larger than a 1-inch tire. This means one set of tires or the other causes the back of my chair to be too high or too low, which throws off both seating position and the front caster angle.

However, there is a hack to work around this.

As you can see in this side-by-side comparison, going from 1-inch to a 2.1-inch tire on the same size rim greatly increases the diameter of the wheel.

A 2.1-inch knobby tire mounted on a 24-inch 540 rim has a nearly identical diameter to a 1-inch tire mounted on a 25-inch 559 rim. Hence, I set my chair up for my 25-inch 559 rims and keep my 24-inch rims with knobby tires in the back seat of my car for easy switching to match the conditions of the day.

This same hack should work on a 25-inch 559 rim and 2.1-inch mountain bike tire matching up with a 26-inch 590 rim and 1-inch tire. I&#;m currently using 2.4-inch knobby tires I got at a local bike shop, and they work fine.

The one size I&#;m not sure this hack works on is 24-inch 540 rims with a 1-inch tire as I haven&#;t had a chance to compare it with the diameter of a 2.1-inch mountain bike tire on the next smaller rim, 22-inch 501. If any readers have, please let me know at .

&#; Bob Vogel

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The Maddening World of Tire Measurements

Let me start by saying that tire size is confusing. Until recently, there were no agreed-upon standards on how to measure a tire, so we were left with a mishmash of measurement systems from different countries. Here in the U.S., we follow the imperial system, which uses inches. What is flawed with this system is that it measures the outside diameter of a tire, and the outside diameter changes based on the width of the inflated tire. That&#;s one of the reasons we&#;ve reached a nothing-makes-sense world where a 25-inch wheelchair rim fits a 26-inch mountain bike tire.

Fortunately, tire and wheel manufacturers across the world have finally gotten on the same page and use a two-number system that does a much better job of keeping your head from exploding. Both numbers are in millimeters and the first refers to the tire width &#; the bigger the number, the wider the tire. The second refers to the inner diameter of the tire. In this system, a 1-inch wide tire that fits a 25-inch wheelchair rim is designated a 23-559, while a 2-inch-wide tire that fits the same rim would be labeled a 54-559 (see below for a list of conversions for common wheelchair sizes).

Imperial Vs. Metric Common Wheel Sizes

Common wheel size conversions are as follows:
22-inch = 501
24-inch = 540
25-inch = 559
26-inch = 590

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The good thing about this system is that you know the tire will fit as long as the second number matches your wheel size. But. That doesn&#;t mean it&#;s always a simple swap. Remember how I said different widths change the outer diameter of a tire? That&#;s important for wheelchair seating.

Wide = Tall

Simply put, a wider tire is a taller tire. These days, most manual wheelchair frames are measured and built to fit narrow tires, so if you put a wider, mountain-bike-style tire on your chair, it will raise your rear seat height.

Take a look at the side-by-side photos below where I show the same 559-rim-size wheels with both a Schwalbe Marathon Plus (25-559) and a Kenda Small Block Eight (54-559). Do you see how much taller the Marathon is on the same size rim? If you look closely, you&#;ll notice the center of gravity changes along with the angle that the casters meet the ground. By putting on a wider tire, I have raised my seat almost an inch &#; a huge change when it comes to chair setup.

• Kenda Small Block Eight (54-559)
• Schwalbe Marathon Plus (25-559)

Many people opt for two sets of wheels: one setup for indoors and pavement, the other for off-road wheeling. That way, you can pop the off-road wheels on if you&#;re going camping, on a hike or to your kid&#;s soccer game, without having to deal with the width and rolling resistance of off-road tires when you don&#;t need them (see Rim-Tire Size Hack above for more info).

It is common to use a size smaller rim with a knobby off-road tire to match the original-sized skinny tire/wheel diameter. Note that when you put on wider tires, you may have to space them farther out so they don&#;t rub on your side guards or clothes. Similarly, you may need to make minor brake adjustments depending on the tire/wheel combo.

For example, if you&#;re currently using a 559 (25-inch) wheel with a skinny tire and you want to switch to the Kobra, you need to buy a 540 (24-inch) wheel to put the Kobra on to keep the chair angles close to the same.

Finding the Right Tire for You

Clearly, there are a lot of factors to consider when selecting tires and every decision comes with trade-offs, but taking the time to consider your tire width, weight and rolling resistance can have a huge impact on your ability to navigate your environment.

Check out these four common wheelchair tires &#; all of which I have used &#; and the pros and cons of each. There are many other options out there, but hopefully this comparison will help you decide which style works best for you and your lifestyle.

Schwalbe Marathon Plus

Intended for city streets, asphalt and sidewalks, this tire offers decent flat protection.

Pros:
&#; Low rolling resistance
on hard surfaces
&#; Flat protection
&#; Lightweight
&#; Narrow chair

Cons:
&#; Sink into soft ground
&#; Slip in snow
&#; Harsh ride quality

Kenda Nevegal

Recommended for off-road conditions where traction is critical, including snow, mud and sand.

Pros:
&#; Superior off-road traction
&#; Float over soft ground
&#; Rugged look

Cons:
&#; Higher rolling resistance
&#; Heavy weight
&#; Knobs can catch on clothing
&#; Wide chair

Kenda Small Block Eight

Recommended for on- and off-road use where you want off road capabilities without sacrificing a lightweight feel.

Pros
&#; Low rolling-resistance for a knobby
&#; Light weight for a wide tire
&#; Black sidewalls

Cons
&#; Mark floor and hands with black
&#; Only available in select sizes
&#; Not thorn resistant
&#; Wide

Kenda Kobra

Recommended for a mix of street and off-road pushing, including gravel, grass and dirt.

Pros
&#; Low rolling resistance for a wide tire
&#; Fast on road and still functional off-road
&#; High-pressure

Cons:
&#; Heavier weight
&#; Gray color and colored sidewalls
&#; Wide chair

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