**5.3 Widened rear wheels concept**

*Public Health in Developing Countries - Challenges and Opportunities*

Forward stability is affected by the size and position of the front castor wheel in relation to the operator's center of gravity. The front caster wheels of the above wheelchair in **Figure 6** are extended to the front to provide forward stability.

The wheelchair resists tipping forward when the castor wheels are stopped suddenly by an object they cannot roll over. Less weight on the front wheels will reduce the rolling resistance of the front wheels, allowing the wheelchair to roll more easily. More of the user's weight on the rear wheels will provide more traction on

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**Figure 7.**

**Figure 6.**

*Extended front caster wheels.*

*Widened rear wheels [12].*

Sideways stability is affected by wheelchair width, thus the need for wide rear wheels. A ratchet arm assembly is operatively connected to each of the rear wheels to enable the operator to propel the wheelchair by that method, should the person so choose. Shock absorbers are fitted to the rear wheels to provide independent wheel articulation, such that if one wheel is to go over an obstacle the other one remains on the ground (**Figure 7**).

The further out to the side of the wheelchair the front and rear wheels touch the ground, the more the chair will resist tipping over sideways. The width of the rear wheels increases their bearing ability such that when utilized in sandy, loose or unstable terrain they do not sink into the underlying terrain and loose traction resulting in the occupant being left stuck. The wheelchair becomes easy to push and there is increased stability. On the downside a wide wheelchair is more difficult to get through narrow pathways. Side way stability is limited due to vertical wheels.

Using the binary dominance matrix method, widened rear wheels concept was chosen for further development. The mechanical design of this concept was developed into the final design in the next section of this chapter.
