Wheelchair wheel placement is a balancing act between three main factors: Ease of propulsion, maneuverability, and stability.
Due to their larger size, the main wheels of a wheelchair have a much lower rolling resistance than the casters. In order to minimize rolling resistance it is important to place the main wheels as close to the center of gravity as possible. However, this will often make the chair less stable. It is also possible to achieve a similar effect by moving the casters further away from the center of gravity, albeit at a cost of maneuverability. The following are three different chair types that take advantage of two of each of the three factors.
A bariatric wheelchair needs to be both stable and easy to propel (for the user or attendant). For this reason, it is advantageous to move the front casters as far forward as possible, maximizing the share of the load on the rear wheels while maintaining stability. This comes of course at the cost of maneuverability in tight spaces.
Long Term Care Chair
A long term care chair needs to be maneuverable and stable. Having the center of gravity roughly between the casters and main wheels while not having an excessively long wheelbase will achieve this. This will increase rolling resistance but since these chairs see most of their use in a facility, this can be acceptable.
PDG Stellar GLT
Since ultralight wheelchair users spend a lot of time wheeling around the community, it is important to minimize propulsion effort while maximizing maneuverability. For this reason most ultralight wheelchairs place the rear wheels as close to the center of gravity as possible, while maintaining a relatively small wheelbase. The loss in rearward stability is often also advantageous for performing maneuvers such as wheelies.
Written by Jim Formby, Senior Mechanical Design Engineer at PDG Mobility
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