Here's a fact: If you show up at my house with black tires on your powerchair, there will be a
problem. No, the problem won't be with me. The problem will be with my wife, who already has me in
the doghouse, and, she'll place you there, too. Why, you ask? Black tires.|
From time to time,
users question as to why powerchair drive-wheel tires are grey rather than black like automotive tires?
Users' reasons for wanting black tires are because black wouldn't show dirt or discolor, giving a cleaner
look, and last longer than grey tires. But, are these points entirely accurate, and why do powerchairs
use grey tires, anyway?
The Hidden Life of Tires
Powerchair clincher tires - as with pneumatic
and foam-filled - seem simple, comprised of a molded piece of rubber. However, there's far more to a
tire than the tread that we see, where the construction and chemistry of tires truly tell the tale of
how they're formed and, ultimately, perform.
Tires begin as two metal rings, called "beads,"
which form the inner ring of the tire. Across the beads, nylon cord is woven, forming the shape of the
tire, creating the "carcass." Once the carcass is complete, it's coated in rubber (polymer). While
the rubber provides no structural support - that's the carcass' job - it does create the "tread," the
varying height and patterned contact area that contacts the ground, creating traction.
construction is fairly straight forward, the chemistry of a tire forms its aesthetic characteristics,
both its color and what it leaves behind. Most tire compounds begin a brownish color. In unprotected
forms, rubber compounds degrade as a result of ozone, the odorless gas that's part of the air that we
breathe. When ozone combines with ultraviolet light from the sun, it dramatically attacks the tire polymer.
To prevent tires from rapidly deteriorating, a sacrificial absorber is used, "carbon black" - which,
fittingly, makes tires black (carbon black is also used in inks, paints, crayons, and polishes).
In outdoor applications such as automobiles, carbon black is essential to a tire's survival. However,
indoors, carbon black is a destructive force. Carbon black not only makes a tire black, but it also
has the potential of marking surfaces that it comes into contact with under force, leaving traces of
For sensitive indoor applications, where flooring shouldn't be marred - homes, hospitals,
food plants, indoor arenas, etc. - nonmarking grey tires are used, where silicon compounds replace carbon
black. These nonmarking silicon compounds are the type that are used to create powerchair clincher tires.
Black Tires Tell All
Most users could put a pair of black tires on their powerchairs,
and roll across a linoleum floor without leaving a mark. But, such initially smooth operation is misleading.
The fact is, like a car leaving a black mark upon sudden braking or acceleration, any quick movements
in a powerchair have the potential to leave a black mark on a floor - how easily marks are made varies
by tire and operation, but under the right condition, black tires mark surfaces. Of especial concern
is that many powerchair tires tend to "scrub" during turns - that is, the tires at one point in a turn
literally twist the tread awkwardly on the floor - and, it's in these maneuvers that the likelihood of
marking increases. Further, carbon black, as a sacrificial additive, reacts dramatically when wet, almost
always leaving black trails and marks on flooring and carpet. (Food plants and hospitals don't just
ban black tires due to potential marking, but also to avoid human contact with carbon black, itself.)
A common assumption is that black powerchair tires wear slower than grey tires. This belief proves
true in automotive tires, when carbon black id used as a stabilizer to decrease deterioration. However,
it's technically another aspects of a tire's makeup - the polymerization of butyl rubber - that changes
the tread wear rate, and in powerchair tires and bicycle tires, there has yet been a definitive study
showing a difference in wear trend between black and grey tires.
Some users also assume that
black tires won't show grime to the extent of grey tires. The fact is, black tires show mud and muck
as dramatically as grey tires, if not more. Dried mud is a light color, and contrasts on black tires,
whereas it blends better with the color of grey tires (this why automotive tire care products are such
a considerable industry - black tires are tough toward maintaining a clean appearance). Furthermore,
socially, others are going to notice seemingly-filthy black tires rolling across their pristine flooring
than they would a more-neutral grey tire.
Users have mentioned the tendency for grey tires to
discolor and become brittle as they age. These suppositions are only partly true, and aren't exclusive
to grey tires. While grey tires do turn darker grey over time, black tires turn brownish during a similar
extended duration. As far as becoming brittle over time, black and grey tires alike may develop sidewall
cracks if left under inflated for long periods, but literal brittleness of the tread (where pieces break
off), isn't a factor - that is, it's not uncommon for drive wheel tires to last years on lightly-used
powerchairs (if the tread isn't worn to its end, the tire typically maintains its integrity).
Carbon black isn't the only way to achieve black tires on mobility products. On
manual wheelchairs, scooters, and powerchairs, dark-colored tires are sometimes used. Such dark-colored
tires, however, are made of polyurethane or self-skinning foam, and, if you look closely, you'll see
that the color isn't pure black, but a milkier shade of black. (Some outdoor scooters, however, do use
black clincher tires, but they are of carbon black, and will leave marks.)
Can't Trust Black
When analyzing black versus grey powerchair clincher drive-wheel tires, the pluses
and minuses become clear. Black tires generally leave marks, especially when wet, show grime, don't
offer improved lifespan over grey tires, and are forbidden in some environments. Grey tires, on the
other hand, are nonmarking, consistent toward disguising dirt, and permitted in all environments.
In the user world, individuals have the choice to put aftermarket black tires on their powerchairs -
and some users don't mind or notice the drawbacks in their particular uses. However, manufacturers can't
responsibly sell black clincher drive tires as a mass-market feature because of the wide range of environments
in which powerchairs are used, knowing the potential hazards of black tires.
Dirty Little Secrets
Getting back to why you can't come to my house with black tires on your powerchair,
it's because my wife knows the down sides of carbon black all too well. Professing how terrible black
tires may prove, I put them on my powerchair for a tradeshow some time ago, to contrast with gold-colored
rims, but never got around to taking them off after the show as needed. Why would I leave potentially
household-damaging tires on my own chair, you ask?
I've left black tires on my powerchair because
I'm an idiotic hypocrite who's too lazy to change tires - at least that's what my wife says when she
scrubs black marks off of our floors and shampoos the carbon stains from our carpeting.
self: Replace black tires with grey tires as soon as possible - black tires are good for tradeshows,
but bad for marriages.
Published 11/05, Copyright 2005, WheelchairJunkie.com