SmartGuard is a “Flat-less” tire technology Non-Marking Black’n’Roll Size: 25"x1". Price is for a set of 2 tires Marathon Plus Evolution Wheelchair Tires operate between 85-140psi and employ SmartGuard. SmartGuard is a “Flat-less” tire technology that protects Schwalbe Marathon Plus Evolution Wheelchair Tire liners from punctures while offering new levels of comfort and superior rollability among pneumatic tires. Now, you can safely navigate through dangerous obstacles like broken glass and count on Schwalbe Marathon Plus Evolution Wheelchair Tires to stay strong. Schwalbe Marathon Plus Evolution Wheelchair Tires are user friendly with 2 grip smooth sidewalls and compatibility with standard tubes. We would also like to introduce Black’n’Roll - SCHWALBE's own revolutionary compound that lets you to wheel these black tires across indoor floor without leaving skid-marks.