Pivotal in creating a power mobility system is determining which drive configuration
would work best for a particular client. Each configuration — front-,
center-, mid- and rearwheel drives — has its pros, and power chair manufacturers
are constantly tweaking technology to compensate as much as possible for each
That said, the location of the drive wheels does significantly impact a power
chair’s performance in an array of situations. Therefore, understanding
the physics of drive configuration is imperative to providing clients with
the vehicles that will work best for them.
Front-Wheel Drive: Bring on the Obstacles!
With its drive wheels in front of the seating area, a front-wheeldrive chair
in effect pulls itself over terrain and obstacles such as curbs. In a SpinLife.com
story, Susan Johnson Taylor, OTR, wrote that this configuration is lauded for
being very stable “for uneven terrain, up and down hills.” Because
a front-wheel-drive chair pulls from the front rather than pushes from the back,
it’s good at handling softer terrains, such as grass.
Foot positioning can also be easier, because there are no front casters to
interfere with foot placement. Therefore, the front-wheeldrive design can keep
feet positioned closer to the body, and can help keep seat-to-floor heights
On the other hand, turning a front-wheel-drive chair, especially for the new
user, can be tricky because “most of the chair is in back (of) you, so
you have to be aware of what is behind you,” Taylor said. Front-wheel-drive
chairs can “fishtail” at higher speeds, so these chairs tend to
have lower top speeds than other drive configurations.
Mid- and Center-Wheel Drive: Turning with Ease
“Mid-“ and “center-wheel-drive” are often used interchangeably,
but in reality they are not exactly the same setup. With mid-wheel drive, the
drive wheels are in the “middle” of the vehicle, i.e., not at the
front of the chair or the back. The drive wheels of a centerwheel-drive chair
are literally in the center of the vehicle — the distance from footplate
to the middle of the drive tire, and the distance from the middle of the drive
tire to the rear caster are identical.
Putting drive wheels in the center or middle of the chair creates a small
turning radius that’s akin to a person turning around in his own footprints.
Because of their ability to basically spin in place, mid- and center-wheel-drive
chairs are highly maneuverable, a prized ability when going through doorways
or turning in narrow spaces.
Mid- and center-wheel-drive chairs are also considered the most “intuitive”
to drive, especially among consumers who have been ambulatory, because the drive
wheels are underneath the seat — thereby mimicking the location of our
feet when we walk.
What are the downsides? Historically, mid- and center-wheel drive configurations
have experienced instability and “highcentering” on uneven terrains
or while negotiating obstacles.
Mid- and center-wheel drives also have more difficulty in climbing obstacles
than front-wheel-drive configurations do. In recent years, manufacturers have
developed technology to compensate, so some mid- and center-wheel-drive chairs
now drive straighter and more smoothly, and are more adept at climbing obstacles.
Rear-Wheel Drive: A Powerful Choice
Rear-wheel drive is known for its power, making it a favorite among consumers
who spend a lot of time outdoors or traversing other aggressive terrains. Rear-wheel
drive has been traditionally capable of offering the highest top speeds —
a plus for the consumer who has to cover a lot of ground, such as a university
campus — and has a reputation for best overall stability in a variety
of different environments.
Its main drawback: With drive wheels in the back, rear-wheeldrive chairs have
larger turning radiuses and therefore larger footprints, since the entire chair
has to clear the corner before making a turn. Rear-wheel-drive is also less
intuitive to learn to operate, because it doesn’t closely mimic the way
people walk. That’s less of an issue with consumers who never ambulated,
including very young children whose first independent mobility is a power chair.
Many young children are put into rear-wheel-drive chairs, said one manufacturer,
because parents find the configuration to be very user friendly — when
approaching a curb that needs to be climbed, caregivers push down on the back
canes, tilt the chair back and just climb over the curb.
A Configuration for Everyone
While rear-wheel drive was the first dominant configuration, created when
manufacturers in essence added motors to manual wheelchairs, mid- and center-wheel
drive are most common today. Yet, rear-wheel-drive is still chosen by some consumers
and clinicians, and a couple of new front-wheel-drive chairs were recently introduced
by major manufacturers.
Ultimately, choosing the best configuration comes down to assessing the client’s
clinical needs as well as his/her environments and lifestyle. Each configuration
has die-hard fans who swear that nothing else is as good. And for their individual,
unique situations — they’re probably right!
I Like the Way You Move!
Go to WheelchairJunkie.com, click
on the Article Index and scroll to the Powerchair section to read Mark E. Smith’s
article “Understanding Powerchair Pivot Points.” Smith, a chair
user and Pride Mobility Products’ consumer research manager, uses diagrams
to explain how and why different drive configurations move as they do.