Published 1/04, Copyright 2004,

Running Flat-Free
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 needs.

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.

Wheelchair 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 " 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.

Co-molded 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.

Solid Inserts
Solid inserts 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.

Semi-pneumatic 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.

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