Different types of tires are available to manual wheelchair users including pneumatic and solid tires. There are advantages to pneumatic tires over solid tires, but they do require regular maintenance of air pressure. Under inflated tires affects wheelchair propulsion.
Sawatzky et al. (2005) investigated the effect of tire pressure on wheelchair propulsion. Tires deflated to 50 and 25 psi from the recommended 100 psi resulted in an increase of energy expenditure of 12.2 % and 24.1%, respectively. Tire pressure does effect energy cost of wheelchair propulsion but not until they are deflated to more than 50% of the recommended inflation.
There is level 4 evidence (from one post-test study: Sawatsky et al. 2005) that tire pressure effects energy expenditure only after the tire has been deflated by 50%.