Schwalbe Marathon Plus Tire, Gray (Wheelchair), 24x1 3/8/37-540. The flat-less tire for wheelchairs. The Marathon Plus is known as the most reliable pneumatic wheelchair tire. The SmartGuard puncture protection layer is made largely from recycled natural rubber. The "Anti-Aging" sidewall can withstand the typical overload caused by low air pressure for significantly longer. Note: When setting the air pressure on the Marathon Plus, always use a pressure gauge. Due to the tire's special construction, a thumb test to "measure" the tire pressure is very unreliable. 24x1 3/8 (37-540) MARATHON PLUS Wheelchair Perf., Gray-Black Wire, 10281540.01 Schwalbe