How to Choose the Best Power Chair Drive Configuration

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 configuration’s cons.

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 low.

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.

This article originally appeared in the July 2010 issue of Mobility Management.

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