By Thomas Renner || Engineers at SoftWheel were recently looking to improve wheel-rim suspension to make wheelchair riding significantly more comfortable and efficient for users. The Israeli company developed four technologies for its SoftWheels suspension to absorb bumps and vibrations and isolate them from the rider’s body. The suspension system fits inside the wheel rims and is anchored by a central hub. No wonder SoftWheels had double-digit sales growth in the the U.S. over last year.

SoftWheel users say the product fives them the freedom to visit places previously too hard to access. “Not being able to leave my house was hard,’’ said Allaina Humphreys, a Chicago mother of three who’s been using SoftWheels for two years. “The freedom to get out and participate in daily life makes me grateful.”

The biggest challenge in designing the SoftWheel was developing a suspension to absorb bumps. Engineers nearly gave up after some early mistakes — but then carefully reanalyzed wheelchair dynamics and began anew. “We knew we couldn’t put the suspension in the chair … so we said let’s put it in the wheel.” Noted SoftWheel CEO Daniel Barel.

“We met many challenges …  including connecting the suspension to the rim and designing a new hub,” added product manager Yoav Satz. More specifically, the wheel includes three suspension arms that are equidistant around the central hub. The arms are inside the rim and absorb shock from any direction.

SoftWheel’s Adaptive Rigidity means the suspension arms stay rigid, but automatically compress when the rider absorbs shock. With its Rapid Shock-Reset technology, the suspension arms are ready to go after one-third of a turn. The quick wheel reset is demonstrated in a video of a drop test compared to a common wheel. In a drop of 15 cm with 110 lb, the common wheel returns to a stable position in 10 sec. The SoftWheel takes just two seconds to become stable. Single-piece Rigid Rims are the final trademarked technology, and they offer as much stability and as fast a ride as the highest-quality regular rims on the market.

The in-wheel suspension activates only when needed — to let the wheel to act as a rigid wheel over flat surfaces and conserve rider energy and forward momentum with reduced bounce on flat surfaces.

Plastic components manufactured by igus complete the SoftWheels design. Engineered plastic L280 bushings called the Marathon Runner and manufactured by German manufacturer igus (with U.S. headquarters in Providence, R.I.) install on the triangular component of the wheels. The plastic bushings provide superior wear resistance in harsh environments or when mated to rough shafts with a very low coefficient of dynamic friction and high wear resistance. The L280 bushings also have a compressive strength of 8,847 psi and at (68°) a tensile strength of 18,130.

SoftWheels have been life-changing for Humphreys, who was injured in a gymnastics accident in 1994. Life in a wheelchair left her with a sore back and spine, and she even had trouble moving around her house. Just days after installing SoftWheels on her wheelchair, she took a trip to City Museum in St. Louis with her husband family. Now, there are no limits to where she can go in her chair.

“I feel like I’m a better partner and mother,’’ Humphreys said. “When I was having such bad pain, I felt like I was a drag. Having SoftWheels makes me feel like I’m an active member of family instead of an observer … it’s life-changing.”