No other design in the history of wheelchairs has proved as successful as the folding vertical X-frame.
First patented in the U.S. in 1937, X-frames have served countless users around the globe for the past
69 years, on manual and powerchairs alike. And, it's no wonder that the folding X-frame is the global
mobility standard - it allows a thin, compact structure for transport and stowage, while easily unfolding
into an entirely functional, full-size wheelchair. With such a blend of functionality and portability,
it's easy to see why the folding X-frame has held its reign for decades as a mobility mainstay.|
the folding X-frame isn't without its flaws. The folding X-frame, as a mechanism, has stability issues,
where the X-frame doesn't completely rigidize a wheelchair - after all, an X-frame is designed to fold
side-to-side, and, as such, is susceptible to energy-robbing frame movement, as with the side frames
moving somewhat independently of the X-frame. Over the years, several manufacturers - Etac, Kushall,
and Quickie, to name three - produced "folding" wheelchairs that did not use an X-frame, striving to
create alternative folding yet rigid structures. While the unconventional folding mechanisms provided
rigidity and stability over a conventional X-frame, the nontraditional folders lacked practicality toward
folding, where the user had to remove wheels or strong-arm mechanisms to collapse the wheelchair (whereas
with an X-frame, simply pulling up in the center of the seat folds the wheelchair, complete). As a result,
users had to make trade-offs, to hassle with a nontraditional folder for the sake of performance, or
give up some performance for the sake of easy folding. Was there a way, though, to maintain the practicality
of an X-frame while optimizing rigidity?
The answer was, yes. Rigidity comes from forming a solid
link between two points. With the seat tubes floating atop the side frames, as with a conventional X-frame,
some play was always involved, where the seat could sway atop the side frames (an affect that was more
prevalent on some models than others based on quality of design) - that is, the two sides of the wheelchair
were never entirely locked out because there was no true rigidizing point between the top points of the
side frames. Rigidizing the tops of the side frames is especially important to address side loads, as
with wheel camber and turning, where the top of the side frames want to pitch inward. If the X-frame
could be entirely seated internally within the side frames rather than on top of them, where the X-frame's
seat tubes parallel the top of the side frames, preventing them from pitching inward, an inherently more
rigid, stable structure could be formed. Put simply, an internal X-frame, where the seat tubes sat beside
the side frames on the same plane, would better prevent side loads from buckling the side frames, better
rigidizing the wheelchair.
In the 1980s and 1990s, European and Asian wheelchair manufacturers moved to internal X-frames, where
it has become a commonplace in their ultralight folding wheelchair markets. Oddly, the North American
market has been slow to adopt the internal X-frame, but with companies like TiLite using the concept
with success for several years, Quickie's bringing the Neon model from Europe to North America (AKA,
the GTX), and Pride introducing its version, consumers, providers, and therapists are catching on to
what most of the rest of the world has known for years - that is, an internal X-frame can dramatically
While the performance benefits of an internal X-frame are clear, the functional
impact is less obvious but profound, fostering easier user transfers. On a conventional X-frame, the
seat tube sits atop the side frame, forming a blunt edge - a blunt edge that's inherently prone to snagging
clothing and body protuberances when transferring. Additionally, a conventional X-frame's seat tube
is a tricky hand-hold point, as the minute one pulls on it, as with a slide transfer, the wheelchair
is prone to folding. By contrast, an internal X-frame resides inside the side frame, eliminating a blunt
seat tube, and, for transfers, allows one to pull on the side frame, not the X-frame, dramatically reducing
the likelihood of the wheelchair unexpectedly folding.
With such meaningful benefits, it's easy
to not find downsides to internal X-frames; however, there are points to consider. When folded, internal
X-frames are typically 1" wider than conventional X-frames - whereas a conventional X-frame may fold
to 4" wide, an internal X-frame may equal 5" (this is specifically due to a conventional X-frame keeping
the side frames in its vertical path when folded, and an internal X-frame dictates that the side frames
remain slightly outside its vertical path when folded). Additionally, drop seating (very rare on active,
high-end ultralight wheelchairs), may have compatibility issues due to mounting hooks and inside widths.
As such, when considering an internal X-frame, relate all of your needs, just as when selecting any
wheelchair, determining the pros and cons toward your mobility needs.
Now, conventional X-frames
remain a wonder of the mobility world - they're simple, sturdy, and functional - and they perform well
under almost all conditions. However, if you're looking for the ultimate in folding performance, think
outside of the box - or, "inside," as it may be - and take an internal X-frame for a spin.
Published 1/06, Copyright 2006, WheelchairJunkie.com