Average Speed - WheelchairJunkie.com

Two cars, a Toyota and a Ferrari, set out on a race, across Midtown Manhattan at 4:00 pm on a Tuesday, having to travel from Chelsea at West 29th to Central Park at West 58th, taking the same route. Which car wins the race?

A nine-year-old boy will tell you that the Ferrari will win because it's “faster” than the Toyota. Yet, as adults familiar with Midtown Manhattan, we know that it's little more than gridlock traffic, with darting cars and pedestrians everywhere, where it doesn't matter how fast your car's top speed is, your average speed may be somewhere around 15 mph amidst such conditions. Therefore, both the Toyota and Ferrari will cross Midtown Manhattan at an arguably identical rate – it's a tie.

Power wheelchairs follow the same rules, where it's often not the top speed that's a deciding factor, but the real-world average speed based on conditions that dictates a power wheelchair's overall performance. An ultra-fast 8 mph power wheelchair may sound impressive, but is it really going to offer dramatically better everyday performance than a 6 mph power wheel chair in many facets of your real-world use?

I first raised this question in my own everyday use. I've always had very fast power wheelchairs, beginning with a 21st Century motor conversion kit some 25 years ago, where my power wheelchairs were always as fast as I could get. However, in recent years, insurer funding cuts have dictated lower-speed models. Whereas 8 mph power wheelchairs were funded in 2003, now funding for similar models typically tops out at 5 mph to 6 mph (based on Group-3 power wheelchair funding coding). Like most users, I found myself going from an 8 mph unit of a few years ago to a newer 6 mph unit, a downgrade in top speed. My ethics are that I use the same production models that my peers and customers use, so when my company's latest rehab model topped out at 6 mph, that's what I went with, too.

By lineage, I still have an older 8 mph model along with the newer 6 mph model (technically, 8.3 mph and 6.2 mph, respectively, per our calibrated, drive-thru lab speed trap, as we strive for any motor speed variation to occur on the high side for consumers), and I use them somewhat interchangeably these days – and I noticed a peculiarity in my everyday use among the two power wheelchairs that I couldn't initially explain. I'm very consistent about getting to my office desk by 7:35 am each morning (a time initially based on walking my daughter to school, but now engrained as simply my schedule). My office is 1.3 miles from my home, and what I found was that when I left at 7:25 am each morning in either power wheelchair – one with a top speed of 8 mph versus one topping out at 6 mph – I was still at my desk at virtually the same time, 7:35 am. How is possible that a 6 mph power wheelchair that has a top speed 25% less than an 8 mph model can cover the same distance in virtually the same amount of time?

The answer, I discovered goes back to the Toyota versus the Ferrari – that is, conditions, where top speed is superseded by the conditions dictated by real-world use and achievable average speed.

By using a stop watch and timing my door-to-door times over several days in both power wheelchairs, I discovered that the real-world difference on my commute was consistently only off by an average 0.6 mph, or 1 minute – that is, the average speed on my 8 mph chair, given the conditions was 6.6 mph, whereas my 6 mph power wheelchair averaged... well... 6 mph. Why was there only a 0.6 mph difference in average speed among the two power wheelchairs, and not 2 mph, as logic would suggest?

I'd say with 34 years of experience, I'm as good as power wheelchair driver as anyone – I can thread a needle at speed, so to speak. Still, many conditions warrant slowing down at an 8 mph high speed – curb cuts, narrow sidewalks, garbage cans blocking a path, railroad crossings, and on and on, are simply to dangerous to negotioate at 8 mph, requiring one to slow down – and those decelerations and accelerations slow the average speed. By contrast, 6 mph is a very manageable speed, where I can run the same obstacle-filled course at wide-open-throttle, never letting off, maintaining top speed. The result, then, is that with required decelerations and accelerations to safely run a challenging course in my 8 mph powerchair, my average speed isn't the top speed of 8 mph, but actually 6.6 mph, whereas with a top speed of 6 mph, I can run the same course at 6 mph flat-out, never letting off of the joystick. That is, in my everyday use, the difference between my 8 mph power wheelchair and my 6 mph version doesn't prove out at a 2 mph difference, but at a barely noticeable 0.6 mph, where conditions dictate the speed, an average speed lower than 8 mph.

Now, here's the important question in this era of tight funding, where if you wish to go from 6 mph to 8 mph on a new power wheelchair, it costs around $1,500 out of your pocket: Do you really need the extra top speed, or does your average, everyday use cancel it out, as proven in my case?

If you're commuting by power wheelchair on bike paths or open spaces where you can safely run at wide-open-throttle for distances, an 8 mph package will certainly prove faster and a beneficial investment. But, if as I describe, your daily routes don't allow wide-open-throttle at ultra-high speeds, a 6 mph top speed will likely serve you just fine. Further, if you drive a van and never commute by power wheelchair, do you really need an ultra-high-speed power wheelchair? Put simply, as a consumer, don't merely consider a high top speed as an end-all, glamorous number with bragging rights, but truly consider your everyday use.

On paper or on the track, a Ferrari may obliterate a Toyota in speed. But, in the real-world, the $125,000 difference in price tag means nothing, where both cars' average speed, as dictated by traffic conditions, can prove the same. And, this truth holds for power wheelchairs: An ultra-high speed is only useful if you have the environment and need to use it.