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Hello all!
Previously, I have written about rolling resistance in manual wheelchairs and the many factors that contribute to resistance to rolling in a manual wheelchair. These factors include the mass of the user and the mass of the system, the weight distribution between the front casters and the rear wheels, and the size and type of casters and tires selected, and the surface on which the wheelchair is used1. For more information on rolling resistance in manual wheelchairs, please refer to the full blog post here.
This month, let's focus on one of the factors that influences rolling resistance: mass of the system, which includes not only the wheelchair, but also the seating system.
Let's start with the wheelchair. How the wheelchair is configured will determine its final weight. When comparing weights of wheelchairs from across manufacturers it is important to read the fine print to determine what components are included in the final weight as each manufacturer's weights can reflect different components. We want to ensure that we are comparing apples with apples; that is, that we are comparing wheelchairs based on similar configuration. When looking at the weights of wheelchairs, we need to consider if the weight is reflective of all components that will be on the wheelchair when the person is propelling it. For example, knowing the weight of the frame alone is insufficient information as a functional wheelchair includes casters, rear wheels, wheel locks, back canes and perhaps hangers, footrests and armrests. It is the overall weight of the fully configured wheelchair that contributes to rolling resistance. Of course, the quality of the components will also be important to rolling resistance so that there is ease of motion to the moving parts and increased durability and tighter tolerances for the non-moving parts, but let's continue our focus on weight.
When we take a closer look at some relative weights of components, we can see how choices affect overall wheelchair weight. For example, a pair of 24-inch 6-spoke mag wheels weighs approximately 1.78 pounds more than a similarly sized lite spoke wheel2. A pair of 5-spoke mag wheels weighs approximately one pound less than the 6-spoke mag set3. Compared to a pair of pneumatic tires, a pair of full polyurethane tires adds approximately 0.7 pounds, while a set of pneumatic airless inserts adds 2 pounds. A pair of high-pressure clincher tires weighs 1.3 pounds less than a pair of pneumatic tires2. The differences in weight continue when we look at the choices of wheel locks, armrests, armrest pads, handrims, and footrests. Of course, weight is not the sole criteria in making selections. Function, positioning and performance are other considerations; however, if there is a choice between two options that would work equally well for an individual, we may consider the impact of any weight difference between the choices.
Sometimes we are concerned about the weight of the wheelchair for transportation reasons; that is, lifting the wheelchair into a vehicle either by the individual using the wheelchair or by a caregiver. To transport an unoccupied wheelchair, we should know how the wheelchair comes apart and/or folds. For example, removing the wheels, assuming quick release axles, may make it easier to lift the wheelchair and wheels separately into a vehicle. The need to lift a wheelchair into a vehicle may be minimized by using alternate ways of getting the wheelchair into the vehicle, such as by tipping the unoccupied wheelchair onto the rear wheels, and using the front casters to roll the wheelchair into the vehicle, while lifting only the load from the rear of the wheelchair into the vehicle.
As I mentioned earlier, it is also the weight of the seating system – the cushion and back support – that adds to the overall weight of a wheelchair. There will be other factors to consider in terms of seating, such as needs for pressure relief, positioning, and stability; however, if weight is of primary concern, consideration should be given to seating selection. For example, the selection of materials in the wheelchair cushion will affect the overall weight of the system. In general, cushions using contained air will weigh less than cushions using foam or gel. Of course, product design and material layering will affect the overall weight of a cushion. A cushion with a fluid insert in a well may weigh less than a cushion with a full gel overlay. Foams with different densities will have various weights. In some cases, products have been designed to reduce the weight of the cushion by minimizing the materials. In selecting a cushion, weight cannot be the only consideration; however, the material and product design of a cushion will not only help to achieve seating goals, but also contribute to the overall weight of the wheelchair and seating system. Lastly in terms of seating, consider the back support. Not only is it the shell and foam that makes up the weight of the back support, but also the hardware that is used to attach the back support to the back canes of the wheelchair. If the goal is to reduce the overall weight of a wheelchair and seating system, consider if options are available in the mounting hardware of back supports that will reduce overall weight.
In summary, the overall weight of a wheelchair depends not only on the frame of the wheelchair, but also on the options and accessories that are selected when configuring a wheelchair. Different choices will affect the final weight of the wheelchair. In addition, the selection of cushion and back support will also add to the overall weight of the wheelchair. Weight is not the only factor that must be considered when prescribing seating and when prescribing a wheelchair, but it is important to recognize how choices made may affect the overall weight of a system, which will influence factors such as rolling resistance and ability to transport a wheelchair. Lastly, let's not forget that weight is only one of many factors that affects rolling resistance in manual wheelchairs.
References
- Tomlinson, J.D. (2000). Managing maneuverability and rear stability of adjustable manual wheelchairs: An update. Physical Therapy, 80(9), 904-911.
- Quickie Q7 Adjustable Order Form, page 6. Retrieved from https://www.sunrisemedical.ca/manual-wheelchairs/quickie/rigid-wheelchairs/q7#support.
- Quickie 2 Family. Endless Options. Retrieved from https://www.sunrisemedical.ca/manual-wheelchairs/quickie/folding-wheelchairs/quickie-2.