Published 10/04, Copyright 2004, WheelchairJunkie.com
A WheelchairJunkie's Guide to Racing Wheelchair Technology (The Epic)|
By Mark E. Smith
Picture this: It's sunny, sixty degrees, with a slight fall breeze behind you, ushering you down
an empty country road on a Sunday afternoon. These are flatlands - maybe just outside the city, or in
the middle of nowhere - and you can see for miles in all directions, past the cows grazing to the right,
beyond the rusty rocks jetting up from the dry meadow on your left, and ahead, to where the smooth, gray
asphalt stretches to a sharp point in the horizon. The only noises that you hear are the compression
of your tires and the exhale of your breath with each push stroke, an audible cadence, a tempo that trips
your cycle computer between seven and nine miles per hour. Every once in a while, you put your hands
on the handle bars and just coast, releasing your muscles, your breath, your mind -- it's just you, your
racing chair, and miles of quiet road.|
Under the right conditions, few recreations are as romantic
as pushing a racing chair, just you, your machine, and the open road ahead. But, while you and the road
are givens, proper racing chair technology is harder to choose, with a lingo far beyond the recreational
pusher's lexicon. However, by understanding the fundamental of racer technology - from cage to compensator
- the paths you push will extend as far as the horizon and beyond.
There may be
no aspect more vital to using a racing chair than proper positioning. After all, positioning affects
balance, aerodynamics, comfort, and biomechanics - that is, proper positioning is a must for optimal
propulsion. The three positions are kneeling, feet-forward, and amputee, with variations in all based
on individual applications.
A kneeling position, commonly used by top athletes, requires that the user kneel on the seat sling,
with the feet tucked out the rear of the chair, captured in a pocket, and the knees slightly elevated
forward. The foremost benefit of a kneeling position is aerodynamics, allowing the user to lean farther
forward in a tuck. Additionally, capturing the entire lower extremities provides a very tight user interface,
maximizing the translation of energy between the user and chair. A kneeling position is most fitting
for users with low-level disabilities and optimal balance and flexibility.
For users with higher-level disabilities, a feet-forward (or, bucket), position is common, with the
knees tucked toward the chest, and the feet ahead of the seat sling, resting on a footplate or strap.
This position is adaptable to the widest range of needs, allowing a combination of leg, knee, and foot
support, and permits accessible transfers. |
For bilateral above-the-knee amputees, an amputee
sling provides appropriate support and positioning.
Whereas the seat sling supports
the racer, the cage is the seat's metal structure, the side guards and frame tubes that surround the
user, essentially forming the overall seating and leg area.
The V-cage tapers sharply at the front
of the seat, where the upper tubes taper down from the top of the wheels, down to the center frame tube.
A V-cage is typically used in a kneeling position, allowing room for the knees, but minimizing frame
material. Because the V-cage optimally forms to the front of the user, it's among the most aerodynamic.
The open-V cage is a wider-cut cage than the V, permitting for more room ahead of the seat sling.
Because the open-V extends farther forward on the center frame tube, it provides for a stiffer frame.
Additionally, the open-V allows more room for feet-forward positions, and enhanced transfer access.
The I-cage has minimal structure ahead of the seat, most commonly used with feet-forward positioning.
While the I-cage allows the most leg room and eases transfers, it is less aerodynamic than other cages,
and can allow more flexing of the front end.
Manufacturers can't agree on where
they measure frame length, with axle-to-axle measurements ranging from 37" to 45", and end-to-end measurements
ranging from 64" to 78". For this reason, it's important to consult the manufacturer's sizing guidelines.
As a general rule, a longer frame runs smoother, tracks straighter, and allows a more aggressive tuck
by the user on downhills. However, based on positioning, arm length, and flexibility, too long of a
frame will hamper performance and safety. Therefore, it's important to confirm the frame length in relation
to each user.
Much like on everyday chairs, axle position relates its placement
forward of the backrest tube, with racing chair axle positions ranging from 4" to 8". The farther forward
the axle position, the better the pushrim access; however, reward stability decreases. Higher-level
disabilities typically require a 4" to 6" axle position, whereas users with optimal balance and coordination
may benefit from a 7" or 8" axle position. There is a formula that measures the upper leg to determine
axle position (upper leg length divided by 2, minus 9, equals axle position); however, other factors,
like balance and positioning should be considered, as well.
Encompassing the front
wheel, fork, steering, and braking, the front end is a racing chair's control center, and should be easily
reached by the user.
Fork mounts are positioned atop the front wheel or behind it, based on the
frame design. The advantage of a top-mount fork is that steering is readily accessible to the user,
up high, where the handle bars are reachable, even when not in a full tuck, depending on frame length.
The disadvantages of a top-mount fork are that it creates a considerably taller frame, raising the center
of gravity, and is difficult for some to surmount when transferring.
A rear fork mount slings the front end and frame low to the ground, enhancing stability, and encouraging
a tight, aerodynamic tuck. Rear fork mounts also ease transferring by lowering the frame, but can make
the steering harder to reach for some users in a feet-forward position (this, however, can be overcome
by a slightly shorter frame length). |
Front handle bars provide hands-on steering, and the
compensator is a spring-loaded device that automatically returns the fork to center when the handle bars
are released from a turn. Additionally, a compensator is adjustable with stops to set the steering to
hold a hands-free turn, as in pushing around a track. In conjunction to the handlebars and compensator,
a caliper brake provides a graceful means of slowing the chair.
Front wheels are available in
18" and 20" diameters. For light-weight users, an 18" wheel serves well, and for heavier users - or
those with a very rearward axle position, loading the front end - a 20" wheel will run smoother, especially
on less-than-ideal surfaces.
Rear wheels for adult racers are available in 26"
and 700C sizes, with shorter adults benefiting from the smaller 26", and average height or taller adults
benefiting from the extra speed of a 700C wheel.
Standard wheel assemblies are wire spokes, and
truly the best choice for recreational racers. $2,000 wheel upgrades to carbon fiber disks, 4-spokes,
and tri-spokes, are fitting for top racers pushing at 18mph on the flats, and hitting 40mph on the downhills;
but, the performance return on the investment is rarely justifiable for recreational racers.
clincher and tubulars are the tire choices for racers. Clinchers are a traditional tire and tube combination
beaded on a traditional rim, whereas tubulars feature the tire and tube encapsulated as a single unit,
glued onto a shallow-wall rim. The benefit of tubulars is that they are super-high PSI for less rolling
resistance; however, they are very difficult to replace after a flat. For the recreational racer, a
clincher tire with rubber tube (not latex), is the most practical tire.
Pushrims are available
in sizes ranging from 12" to 16" diameters. Much like gearing, the smaller the pushrim, the more strength
required to propel the chair, but the more speed achieved. The most practical handrim sizes on a 26"
or 700C wheel are 14" to 16". For use on a lot of flat roads or tracks, 14" may be the most fitting,
whereas for rolling hills and varied road use, a 16" gives a tad more leverage for climbing. To maximize
glove traction, pushrims are wrapped in friction tape or covered by a glued-on tire. A coating of friction
tape is usually standard, with a tire-coated pushrim costing $85 to $150 at the time of the build; however,
tire-coated lasts longer than taped, and offers better grip.
Racing chairs usually carry 11-
or 12-degrees of wheel camber, both for ergonomics and stability. Taller users, those who sit high in
the cage, and those pushing track may go as far as 15-degrees of camber.
can't you push a racing chair without gloves, you really can't push without the right gloves. Harness
Designs gloves run around $90, and are built with contact surfaces to maximize grip and durability, both
for traditional and quad pushing techniques. Alternatively, some still prefer the old-school method
of handball gloves strategically wrapped in athletic tape. With the hands protected for battle, one
shouldn't forget about the brains of the operation, either, and always wear a helmet.
this: It's cloudy, thirty-nine degrees, with a winter wind in your face, testing you on a Saturday
morning. These are steep hills - maybe just outside the city, or in the middle of nowhere - and you
can't see more than a quarter-mile past the mist, merely guided by the white line marking the shoulder
of the black asphalt road. The only noises that you hear are the compression of your tires and the exhale
of your damp breath, which you can see with each push stroke, a tempo that trips your cycle computer
between four and six miles per hour. Every once in a while, you glance at your pumping arms, and pick
up the pace, pushing with more strength than ever before, knowing that over this hill there are five
more miles of road waiting for your quiet conquer.