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When it comes to wheelchair wheels, there is a tremendous amount of confusion. I am certainly not an expert on the subject, but I will pass on some of what I have discovered.
Based on the dimensions of the wheel RIM, there seems to be four common adult sizes. They are 501, 507, 540, 559, 590. Where the number represents the millimeter size of the rim. 507, 559, and 590 are also bicycle sizes which means you can use bicycle inner tubes and tires. 501 and 540 are strictly wheelchair sizes. Wheels are also described as 22", 24”, 25” and 26”, where the number represents the general outside size of the wheel. Rather than being a measurable dimension, think of the numbers representing x-small, small, medium, and large with a lot of leeway in the actual dimensions.
501 is 22" wheelchair
507 is 24” wheelchair and 24” bicycle.
540 is 24” wheelchair.
559 is 25” wheelchair and 26” bicycle.
590 is 26” wheelchair and 26” bicycle.
If you have a 501 (22") or 540 (24”) wheel, you must get a wheelchair tire. If you have any of the other sizes, you can use a bicycle tire. Wheelchair tires are either pneumatic (air) or solid. Solid wheelchair tires are usually 24” x 1” and 24” x 1 3/8” where 1” and 1 3/8” represent the width of the tire. Note that a wider tire is also a taller tire in terms of diameter (height). Solid tires have been shown to have significantly more rolling resistance than pneumatic. Thus requiring more effort to push.
Pneumatic wheelchair tires are usually 24” x 1”, 24” x 1 3/8", and 24” x 2”. Think of them as 1” is a street tire, 1 3/8” is a hybrid tire (medium tread), and 2” is an off-road (knobby) tire. The diameter of the tire will affect the geometry of your wheelchair. Smaller diameters will lower your seat height and tilt the backrest into a reclining position (angle > 90 degrees). Larger diameters will raise your seat height and tilt your backrest into a forward position (angle < 90 degrees). In addition, wider tires require a longer axle and spacer in order to move the tire sidewall away from the side of the wheelchair. Therefore, it makes sense to have a complete wheel set of wheels and axles for switching to knobby tires for rough terrain. If you have brakes, different wheel sizes will require brake adjustment or requiring not using the brakes.
If you have a 25” x 1” /559 wheelchair wheel, the outside diameter is about 24 ½” which is close to the size of a 24” x 2”/540 knobby tire (24 ¾” outside diameter). Therefore, it makes sense to switch between these two wheel sizes which will have a minimal impact on your wheelchair geometry and brakes. I use this system for snow when I only want to switch my drive wheels for better traction.
But for rough terrain, I will use a trike wheel. The typical trike wheel such as the Free Wheel or Front Wheel, will raise your front casters off the ground which tilts your chair into a reclined position. Therefore, having larger drive wheels will counter this issue. Assuming the trike wheel raises your front casters by about 2”, you can raise the height of your wheelchair by putting on 26” knobby bicycle tires.
Note that these larger diameter tires will have a significant impact on your brakes. They will also change your pushing dynamics since more wheel will be available to grab and push.
Therefore, the wheels you use on your wheelchair require some forethought, planning, and expense. Unfortunately, this complication explains why most wheelchair users only have one set of wheels which is less than optimal for rough terrain or slippery conditions. In my opinion, full time manual wheelchair users should have multiple sets of wheels with different treads. No different than active able-bodied people with multiple sets of footgear depending upon the conditions and intended use.
When you buy wheelchair tires, you pay “wheelchair” prices and have limited options. When you buy bicycle tires, you pay “bicycle” prices and have a wide variety of options. Bicycle tires also have a 2nd number with denotes the width of the tire. Where 25mm equals 1” in width. Therefore a 25-559 is a 26” x 1” bicycle tire which fits a 25”/559 wheelchair. A 50-559 tire is 26” x 2” bicycle tire which also fits on a 25”/559 wheelchair rim. Wider also means taller which means a greater diameter wheel.
Remember that a 26” bicycle tire could be either 559 or 590 in the same way that a 24” bicycle tire could be 507 or 540. And a 25” bicycle tire does not exist. A 25” tire is a wheelchair tire which is a 559. But if you go to a bicycle shop and ask for a wheelchair tire, you are likely to get handed a grey 24” x 1 3/8” (540) since they are the most common.
Note: I have been told that you can also put on a knobby tire on a 501 (22") which is approximately equal in height size to a 540 (24" x 1") wheelchair tire. I have no personal experience this doing this.
In summary, it is important to understand the impact a tire will make on wheelchair's configuration and propulsion, and hence your resulting mobility. The type of tire you use will make a large difference on your ability to navigate different types of terrain and environments.
For more on the subject, check out: