Wheelchair Design: Race Version

I notice, almost without exception, that when people find out I’ve done some wheelchair design work, there is a disproportionate interest in hearing about it.  In some ways I can understand bike people’s interest in wheelchairs.  There are many similarities between bikes and wheelchairs:  mobility, freedom, self locomotion, and the augmentation of physical capability, to name a few. 

Back in the early ‘90s I spent more than 2-years working fulltime—and then some—on two wheelchair projects for Merlin Metalworks in partnership with Halls Wheels.  The reason I am posting about it here is twofold:

First:  these two projects had a significant impact on my interest in bike fit and bike performance design—and therefore in many ways it has affected Seven Cycles’ design philosophies.

Second:  these are projects that are long ago closed, so I can divulge project details, planning, and challenges—something I can’t do with current projects, for obvious confidentiality reasons.  And, these projects had a very full scope, including:  basic research, development, design, and commercialization.  So they are potentially interesting case studies in product design and biomechanics.

The two wheelchair development projects of which I was a part were:

1. A titanium racing wheelchair design
2. A titanium ‘everyday’ wheelchair designed for sports including basketball, rugby, and tennis

I’ll post a bit about the racing chair now, and later about the everyday chair; the everyday chair was much bigger project.

When we began the project we simply followed to very smart lead of Bob Hall.  Bob is considered the father of wheelchair racing.  In 1975, at the age of 24, he was the first sanctioned wheelchair racer in the Boston Marathon; and the Boston Marathon was the first major marathon to permit wheelchair competitors.  In addition, Bob has played a critical role in the development of wheelchair racing.  He wasn’t just an athlete, he was a design innovator.  We at Merlin were fortunate to have the opportunity to work with Bob. 

Together we developed a titanium racing wheelchair that played an important part of changing the racing landscape.  When The Scientific American Frontiers television program interviewed Bob and I, they called it, “A design revolution.”  I’m not sure about that but, in the chair’s first official race outing, Craig Blanchette—pictured here—set a one-mile world record.  Not too shabby.

This titanium racing chair was new in many ways.  While we were designing our titanium chair, Bob was redesigning, in tandem, his steel racing wheelchairs.  We all agreed that we would question every existing standard for wheelchairs—nothing would be sacred.  We asked a lot of stupid questions and didn’t know enough to know what was or wasn’t possible.  Because of this we came up with some new ideas that had a big impact on wheelchair design and overall attainable speeds.  We tried to rethink every element of a classic racing chair.

We would meet pretty much every day to compare notes and see how we could apply what the other had evolved.  Bob was taking ideas from our experience with titanium and with bicycles.  I was voraciously consuming everything he had to teach about wheelchair design, steel brazing, and his tricks and techniques for fitting his athletes.

Granted that if you don’t know wheelchairs, most of these design changes won’t mean much.  Regardless, some highlights include:

• A simplified headset and fork system that did away with the standard bicycle headset; that part was completely overbuilt for a racing chair.  The front wheel on a racing chair sees barely any load at all; we ended up reducing the weight of the front end by nearly half a lbs.  We designed it from the ground up—rethinking everything from the axle, how it attached to the fork, the fork shape and material, and even the bearing surface.

  

• A new axle system the greatly increased the rigidity of the system; wheelchair wheel axles see a tremendous amount of torque—they call it scrub.  This scrub, or twisting of the wheels steels a lot of speed.  Essentially, the wheels aren’t going in the same direction.  So, the stiffer the axle and connection between the wheels, the less scrub that can occur.  We used a 1.5” through axle.  Older designs had two separate axles that relied on the rigidity of the rest of the frame to maintain wheel alignment.  This new system was a lot lighter and stiffer because the axles were directly connected.
• An infinitely adjustable camber adjustment system that allowed for perfect camber adjustment.  A long story to explain here.
• Employing titanium as the frame material.  We were able to create a very stiff oversized chassis while leveraging some of titanium’s durability to allow flex in some areas so as to enhance comfort.  And, of course, we were able to make the chair a lot lighter than its steel counterpart.  The entire design went from 17.5 lbs. to 12.0 lbs.—nearly a 30% improvement.

All of these changes added up to a 20-second speed gain per mile in the Boston Marathon from 1990 to 1994—an improvement of more than 10%!  At their peak in the mid 1990s racers were reaching average speeds of 19.75 miles per hour in the Boston Marathon.  That is incredibly fast for an un-geared, manually powered vehicle, with no real drafting to speak of.  It was an exciting time in wheelchair racing evolution.  In fact, the women’s record from 1994 still holds, while the men’s record from 1994 was improved on by about 3.5% a decade later.

I’ll post about the kinesiology, ergonomics, and biomechanics of the racing chair in a subsequent post—that’s the part that really effected bike design for me.  Of course, the results I mentioned here helped us know we were on the right track.

Rarely does a day go by where I don’t think about that 2+ years of my life and its lasting impact on the way I think about bike design.

Comments

[Mike]

I do marathons in a racing chair that evolved from this original design, and just wanted to say that this is a great article. Looking forward to read the follow up article about the ergonomics and biomechanics of the racing chair.