Manual Wheelchairs - World Health Organization

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Table 2.7. Aim: to improve manoeuvrability over soft ground Advantages Disadvantages By increasing the width, diameter and softness of the castor wheel to increase the contact area, thus helping to prevent the wheelchair from sinking into soft ground a n A wide wheel with a raised point on the centre of its tread can combine low rolling resistance on hard surfaces with good flotation over soft ground. n less weight on the front wheels will reduce the rolling resistance of the front wheels, allowing the wheelchair to roll more easily. desIgn and productIon I 51 n Increasing the contact area of the castor wheel with the ground can make it more difficult to turn, especially in tight, slow turns. By increasing the width, diameter and softness of the rear wheel to increase the contact area, thus helping to prevent the wheelchair from sinking into soft ground a n larger-diameter rear wheels can make it easier to roll over rough terrain. n In many less-resourced settings, 28-inch bicycle tyres are widely available; 26-inch tyres are somewhat less common, and 24-inch tyres are more difficult to find. n Wider and softer rear wheels can make it more difficult to turn, especially in tight, slow turns. n larger-diameter rear wheels make the wheelchair more difficult to transport. By moving the front castor wheel(s) forward to reduce the weight on the smaller castor wheel(s) and make it less likely to sink into soft ground n More of the user’s weight on the rear wheels will provide more traction on the rear wheels to drive through soft ground. n Overall wheelchair length is longer, making it harder to manoeuvre in confined spaces. See also Table 2.4 for related effects. By moving the rear wheels forward in relation to the user to reduce the weight on the front castor wheel(s) and make it less likely to sink into soft ground n More of the user’s weight on the rear wheels will provide more traction to the rear wheels to drive through soft ground. n reduced tendency to turn downhill on side slope, which requires less energy from the user to correct for downhill turning. n User has better access to the hand rim and a longer push stroke, making it easier to push the wheelchair and better for the upper extremities. n easier to perform “wheelies” to negotiate obstacles. n Wheelchair is easier to manoeuvre in confined spaces. n reduced rearward stability. By using rear wheels with knobs, such as those on mountain bike tyres, to increase traction on soft ground and keep wheels from slipping n Spikes or knobs on tyres cause additional flexing of the tyre and thus higher rolling resistance. n Mud will collect more on tyres with knobs than on smoother tyres. a Substituting larger castor and/or rear wheels on a wheelchair not designed to take them can change important functional performance features, including seat angle, castor barrel angle and seat height (user’s centre of gravity). 2
52 I guIdelInes on the provIsIon of manual wheelchaIrs In less resourced settIngs • Manoeuvring over raised obstacles, such as bumps, kerbs or rocks, depends on many factors. The size of the castor wheel, the distance of the castor wheel from the user’s centre of gravity and the springiness of the castor wheel all have a significant effect. Castor flutter is also a result of hitting bumps at speed. Ways of improving manoeuvrability over raised obstacles and their associated advantages and disadvantages are shown in Table 2.8. Table 2.8. Aim: to improve manoeuvrability over raised obstacles Advantages Disadvantages By increasing the distance between the front castor wheel(s) and the user’s centre of gravity See Table 2.4 for related effects. By increasing the diameter of the castor wheel See Table 2.7 for related effects. By increasing the diameter of the rear wheel See Table 2.7 for related effects. By increasing the amount of deflection/springiness of the castor wheel n A softer wheel can make it more difficult to turn, especially in tight, slow turns. n A pneumatic castor wheel can be difficult to repair or replace. Note: Although users with advanced mobility skills can compensate for a wheelchair’s lack of manoeuvrability over objects by moving their body posture to balance the wheelchair, unseen obstacles can put the user’s safety at risk.
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Barriers to participation of users
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References polIcy and plannIng I 12
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Other resources Cooper RA. Wheelcha
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Manual Wheelchairs - World Health Organization

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