The Nu-Teck Airless Bike Tires, which can be mounted on most wheelchairs, are flat-proof, leak-proof, and maintenance-free. Instead of being inflated, they are made with microscopic air cells trapped in a polyurethane matrix similar to the material in the soles of running shoes. Their weight and rolling resistance on most surfaces are about the same as that of inflated tires. They are a complete tire. Most sizes available.