subject: What You Should Know About Wheelchair Wheel-Camber [print this page] What You Should Know About Wheelchair Wheel-Camber
What You Should Know About Wheelchair Wheel-Camber
Tilted-rear-wheels or camber, a popular feature on racing wheelchairs, is being seen more and more on wheelchairs that are used for activities of daily living. One of the advantages of camber is that it provides better lateral static stability for the wheelchair as a result of the greater distance between the low/bottom-points of the two wheels. This is especially advantageous when frequent sideways movements are needed, as in wheelchair-basketball.
Also, as a result of the larger wheelbase, the downward turning-moment of the wheelchair decreases on a side-slope. It can be described as an angling that brings the top of the wheels closer to each other. Athletes who wished to improve wheelchair-handling characteristics and stability first introduced camber into wheelchairs.
In a study conducted in The Netherlands, eight, non-impaired subjects participated in a wheel-chair exercise-test using a motor-driven treadmill in order to study the effect of rear-wheel camber on wheelchair ambulation. The test consisted of four runs with rear wheels in 0, 3, 6, and 9-degrees camber at speeds of 2, 3, 4, and 5 km/hr. There were no significant effects upon oxygen-usage, heart-rate or mechanical efficiency. The kinematic parameters of push-time, push-angle and abduction showed differences between 3 and 6, camber. The relationship between the findings, using surface EMG results for six shoulder muscles was an integral part of the study. For one subject, data were extended to study the angular velocities of shoulder and elbow.
Besides the greater stability of cambered wheelchairs, cambered rear wheels provide an easier reach to the hand-rims and less hampered arm movements during push and recovery movement, leading to a less strenuous propulsion technique. It is also suggested that camber would be more efficient due to the effective application of force and lower losses as the result of less arm abduction and stabilization. A study on wheelchair characteristics during the 1980 Paralympics showed a trend of increased success of the athlete with increasing camber. The most successful athletes had wheelchairs with a camber.
The amount of camber introduced is measured in degrees. The higher the number, the more camber or angling. Some more expensive models of wheelchairs have methods of adjusting the camber. Camber-adjustment is most often accomplished by inserting a different "camber-bar" that alters the angle. Further, the axle-plate can be adjusted for increased camber-angle. Certain specific models of wheelchairs with a fixed camber do not allow the altering of the camber-angle. In these cases, the camber-angle may be specified when the wheelchair is ordered except in the case of certain "low-end" wheelchairs.
As camber is increased, the width of the wheelchair across the bottom increases. This adds lateral stability to the system by increasing the wheelchairs footprint. If too much camber is added, there may be a problem getting through doorways. The amount of camber required for ordinary, daily use is not the same as that that is required for wheelchair sports.
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PROS
The wider footprint adds lateral stability to the wheelchair.
Redirects forces to soften the ride.
Places the push rims in a more ergonomic position for pushing. It is more natural to push down and outward.
Protects the hands when pushing in tight areas since the bottom of the wheels will make contact first with walls and doorframes.
Less strain on shoulders since the plane of the wheel is closer to that of the shoulder.
Makes turning quicker.
Gives the wheelchair a sportier look.
CONS
Wheelchair will be wider.
May add cost to the chair.
Excessive camber may cause the wheels to rub against the arm-rest(s), side-panels or against the user.
Diminished traction and uneven tire wear on a conventional tire.
NOTE: Conventional tread placement is centered on the tire. A cambered-tire rides on the inside edges of the tire. Some manufacturers make tires with offset treads to compensate for cambering.
Footnotes
1. abduction the movement of a limb away from the midline of the body. Abduction of both legs spreads-the-legs. The opposite of abduction is adduction. Adduction of the legs brings-them-together.
2. EMG Electromyography. The study of risks in nerves and muscles in the human body.
