I recently saw a gentleman in a Sport Wheelchair exit an elevator, and I commented, “Do you know that wherever you go, you’re pushing uphill?”
He looked at me like I was insane, and kept pushing, without response. However, he shouldn't have dismissed my seemingly off-the-wall comment so quickly, for he had ten-degrees of toe-out on his rear wheels, and his caster housings were angled back by another five-degrees. To top it off, as he rolled away, giving me a dirty look over his shoulder, I notice that his right rear wheel stuck out two inches farther from the frame than his left wheel. Like I said, wherever the gentleman went, he was pushing uphill.
Users are often concerned with a Sports Wheelchair’s weight and design; however, few aspects affect a Sport Wheelchair’s performance more than proper wheel and caster alignment. More often than not, users, dealers -- and even manufacturers! -- ignore the importance of Sport Wheelchair alignment, and the result is that a huge percentage of users -- in my observation, three-quarters -- are using Sport Wheelchairs that are out of alignment, which, even at very minute levels, doubles a chair’s rolling resistance. Still, it is a problem that, once a user understands the principal factors of alignment, is correctable, turning a chair from a slug to a stallion.
To begin checking your Sport Wheelchair’s alignment, measure the distance (offset), between the top of each rear wheel and the backrest. The distance should be equal on each side of the chair:
If the distance isn’t equal, if one wheel sticks out farther than the other, the chair will pull to one side. To correct unequal offset, most chairs allow for axle sleeve adjustment (the hole where your axle attaches to the frame). By adjusting the sleeve inward or outward as needed, you can adjust the wheel’s distance from the frame. Note, however, depending on the amount of camber and user weight, flexing occurs, so you may not want an offset less than an inch, as once the chair is in use, the wheels may rub on the backrest (under most conditions, I suggest a 1 ½” offset).
The most common alignment mistake users, dealers, and manufacturers make is in ignoring “toe-in” and “toe-out.” The rear wheels of a Sport Wheelchair are like feet. To function most efficiently, like one’s feet, a Sport Wheelchair’s rear wheels must point straight ahead, paralleling each other. If the front of the rear wheels turn inward -- like someone who is “pigeon-toed” -- it’s call toe-in, and if the front of the rear wheels turn outward -- like a penguin -- it’s labeled toe-out (interestingly, the term is the same in medical usage referring to foot alignment). Under no circumstances should your chair have any toe-in/toe-out -- that is, your wheels must be parallel to one another -- and, as little as two-degrees of toe-in/toe-out from the parallel position, according to a study by the University of Virginia, doubles a wheelchair’s rolling resistance (two-degrees is too small of deviation for most to visually detect, but it can ruin a chair’s performance).
To determine if your rear wheels suffer from toe-in/toe-out, align both rear wheels so two spokes on each wheel are parallel with the ground, pointing toward 9 and 3 o'clock. Take a measurement from wheel to wheel, spoke to spoke, between the rearmost place on the wheels, then take a measurement across the same span at the front of the wheels. If the width measurements are the same -- let’s say, 20” rear, 20” front -- your chair has perfect alignment. However, if you end up with different widths -- say, 20” rear, 22” front -- your chair suffers toe-out, or toe-in if closer in the front.
Toe-in/toe-out is caused by changing the angle of the axle mount on a chair with cambered wheels. The principal of camber is that the wheels are closer at the top than the bottom, based on a ninety-degree angle with the ground -- meaning that the narrowest and widest widths between the wheels are at 12 and 6 o'clock, respectively. Now, here’s the tricky part: Camber is only productive if the axle mount remains at a ninety-degree angle to the ground. If you raise or lower a Sport Wheelchair’s frame in the front or rear, changing the frame’s angle, the axle mount’s angle changes, too, thereby changing the wheel’s camber location. For example, if you lower the rear of a chair by moving the axle/camber plate up two holes on the frame -- which changes the angle of the axle mount, as well -- the camber points of narrowest and widest widths shift from 12 and 6 o'clock to 10 and 4 o'clock, making your rear wheel’s distance apart slightly wider at the front than the rear, creating toe-out.
To correct toe-in/toe-out, you have to return the camber point to ninety-degrees (or, practically speaking, as close to ninety-degrees as possible). The way to achieve realignment on a frame that sits at an angle is through adjusting the axle mount, itself (although the entire axle mount may not sit at ninety-degrees, you can return the camber point to ninety-degrees by adjusting specific areas of the axle mount). On a Sports Wheelchair with an axle/camber plate, add washers to the end of the mount opposite the flared out side of the wheel:
A Sport Wheelchairs with an axle/camber tube also may need toe-in/toe-out correction, which may be accomplished by rotating the axle/camber tube in its mount -- forward rotation corrects toe-out, and reward rotation corrects toe-in.
Now that your real wheels are aligned, it’s time to turn to the caster housings (also called barrels or journals). Unlike the complexities of rear-wheel alignment, caster housings follow only one foolproof rule: No matter what angle your frame sits at, the caster housings must remain at a ninety-degree angle to the ground -- put simply, the housing must be straight up and down.
Most Sport Wheelchairs feature bolt-on caster housing, which are angle-adjustable by means of slots, eccentric bolts, or cams. To confirm that the caster housing is at ninety-degrees to the ground, you can use a bubble level, carpenter’s square, or, my personal favorite, the spine of a hard-cover book.
I’d be leading you on if I suggested that wheel alignment is simple business. Yet, with a basic understanding, astute observation, and a Saturday afternoon, you can have your Sport Wheelchair performing its best.