Wheelchair Profiteering, Part VIII: Wheelchair Design and the “Weakest Link” - Erik Kondo

A bicycle with a high quality frame could last decades with regular replacement of components. On the other hand, manual wheelchairs are expected to be replaced every five years (assuming the person has health insurance or the funds to pay for replacement).  Why the difference in lifespan?

A manual wheelchair in many ways is comparable to a simple bicycle. So how is it that its lifespan is so much shorter? Most wheelchairs spend their days inside, move slowly, and for relatively short distances. Bicycles are used outside, at comparatively high speeds, go long distances and on terrain that typically involves potholes, cracks, and bumps.

Rather than thinking about how to extend the life of a wheelchair. Let’s determine what it would take to reduce the life span of a bicycle to five years. In other words, turn the bicycle into a typical wheelchair.

Since bicycles' use modular sections with continuously replaceable components, the most effective way to limit the life cycle of a bicycle is to reduce the useable life of the main frame. Failure of the frame will necessitate bicycle replacement. The complexity or extent of the bicycle frame is a function of its original design. By incorporating aspects of the bicycle that will likely fail in five years into the frame, you effectively limit the life of the frame and thus the entire bicycle. The aspects of the frame that fail become the “Weakest Link” of the bicycle.

Since the failure of a frame weld could be catastrophic and injure the rider (creating a lawsuit), the frame should fail in a consistent and slow manner. For example, the housing that contains the wheel axle could progressively deteriorate causing the wheel to wobble worse and worse over time. Since the housing is an integrated part of the frame, it cannot be repaired. Thus, the entire bicycle would need to be replaced to fix the wheel wobble.

Here is where our thought experiment ends and reality sets in. No company would design a bicycle with this type of “Weakest Link”. Once word got out, no consumer would buy it.  But wheelchairs are designed this way. The caster housing and the frame/caster connection are the “Weakest Link” of a wheelchair. Modern active wheelchairs integrate casters into the frame in such a manner that caster failure and related problems are prime causes of wheelchair replacement.

It makes no sense that the foreseeable breakdown of a relatively simple component of a wheelchair would end its useful life unless there was no desire to extend the life of the wheelchair the first place. A wheelchair with a failed integrated caster housing cannot be easily repaired. It is time for a new one. Another wheelchair is produced and sold (more profit!) rather than repaired (less profit!).

In order to extend the useful life of wheelchairs, you must design to mitigate the “Weakest Links”. They need to be part of modular sections. Now when they fail, they can get replaced, and the life of the wheelchair goes on. In other words, get rid of the "Weakest Link" problem entirely.

The lifespan of a wheelchair is proportional to its ease of repairability. Its repairability is determined by its design. If a wheelchair model typically lasts only five years, it is because it was designed to be that way.