Published 1/04, Copyright 2004, WheelchairJunkie.com
A WheelchairJunkie's Guide to Flat-Free Tires
By Mark E. Smith
"Flat-free" tires are as old as the modern wheelchair, itself. But, as mobility technology flourished
over the past three decades, flat-free tire technology equally evolved, dramatically broadening the definition,
construction, and performance of flat free tires. Whereas flat-free once meant a solid rubber tire,
today' definition can range from a foam filling to a poly urethane tread to a rubber insert, and it's
important for the consumer to understand which construction and material best meets his or her performance
On today's powerchairs, foam-filled tires, especially on the drive wheels,
are the most popular flat-free solution. The foam-filled process uses a standard pneumatic tire - minus
the tube - and via a mold-in process, fills the tire's cavity with foam, replicating a fully inflated
tire. The foam may vary in density depending on the required weight capacity, but most equate to a ride
similar to the maximum PSI rating of the tire -- that is, foam-filled tires provide a somewhat firm ride.
Because foam-filled tires compare to a forever-inflated tire, a split-rim is required for installation
(forget using a flat-head screwdriver to pry these tires on a one-piece rim!). The foremost benefits
of foam-filled tires are that you receive the same optimal tread as a rubber pneumatic tire, and because
foam-filled tires bead properly, they won't roll off the rim in high-speed, high-stress applications.
The lifespan of foam-filled tires equals that of a properly maintained pneumatic tire.
Junkie Tip #16,738: If you're storing a powerchair or scooter with foam-filled tires for a prolonged
period, place it on blocks, with the tires approximately ½" to 1" off the ground, preventing flat spots
on the tires from sitting stationary.
Poly Urethane (PU)
PU tires are the most common
flat-free tire on manual wheelchairs, used on both rear wheels and casters. PU tires are a highly-resilient,
one-piece molding that's fairly lightweight. PU tires come in a variety of tread patterns, with molded
air pockets to soften the ride characteristics. With such a resiliency, PU tires may pry onto a one-piece
rim, with a secure bead (they're typically flawless on manual chairs, but may roll off the rim on a high-speed
rear-wheel-drive powerchair caster). The lifespan of a PU tire is often three or four times that of
a traditional rubber tire, never needing replacement in some cases.
tires are most commonly found via powerchair casters and low-end manual wheelchair wheels, where a plastic
rim and molded-type tire are permanently bonded as a single unit. Co-molded tires are especially useful
as anti-tip wheels, where durability is more important than ride characteristics. A version of this
genre is the solid over-molded foam caster - most common in 8" casters on mid-range powerchairs - which
offers durability with an enhanced ride characteristic. Co-molded tires have an exceptional lifespan,
but the entire wheel assembly requires replacement when worn.
were the predecessor to foam-filled tires, filling the void within a pneumatic tire, and allow use on
one-piece rims (a special tool is required for installation on one-piece rims). Because solid inserts
are. . . well. . . solid - or, solid rubber - they add considerable weight to the tire, decreasing performance
in manual wheelchairs. On powerchairs, solid inserts may degrade quite rapidly, leaving you with somewhat
flat, flat-free tires (because the inserts float between the rim and tire, high-weight and torque applications
can stretch and twist the inserts). On manual wheelchairs, however, solid inserts allow the use of a
standard pneumatic rubber tire, offering improved traction over a PU tire.
tires and inserts feature molded-in air pockets, much like the air pockets in the soles of athletic shoes,
providing a slightly cushioned ride. Found in forms ranging from poly urethane tires to inserts, semi-pneumatic
tires never need air maintenance, nor will they become flat when punctured, making them truly flat-free.
The important distinction, however, is that while all semi-pneumatic tires are flat-free, not all flat-free
tires are semi-pneumatic, as with solid rubber tires.
Indeed, who knew there were so many
factors and choices in merely wishing a flat-free tire? But, by selecting the right tire for the right
application, you can stroll the boulevard, ensured that your chair is both flat-free and trouble free.