The BT-X is a lightweight sport wheelchair designed for use by individuals with mobility disabilities or spinal cord injury. It is intended for indoor and outdoor use on a variety of terrains, including unpaved paths and beaches. To facilitate this versatility, the BT-X is designed to fit multiple wheels and casters in addition to those include with the standard model. FRAME: Aluminum alloy frame and forks. SEAT (WxD): 14, 15, 16, 17 or 18 x 14, 15, 16, 17 or 18 inches. Backrest height is available from 5 to 20 inches in 1-inch increments. The backrest angle is adjustable from 80 to 100 degrees. UPHOLSTERY: Laminated carbon fiber sailcloth adjustable by tension cord. CASTERS: Frogs Legs Ultra Sport casters (DxW): 4 x 1.5 or 5 x 1.5 inches are standard. For off-road use, 6 x 1.6 inch soft casters are available and can be rotated forward on the frame. For use on the beach custom 9 x 5 inch balloon tires are available to be mounted in the front. WHEELS: Spinergy LX or SLX Sport wheels (25-inch diameter) with anodized handrims and pneumatic tires are standard. Two degrees of camber are standard. The SLX Sport wheels may also use the Schwalbe Nobby Nic tires for off-road use. For beach use, custom 4-inch wide wheels are available. FOOTRESTS: Single-piece footrest. WEIGHT: 14 pounds (frame only). WARRANTY: Lifetime limited warranty on frame.