This is your entire wheel kit*, not just the rubber tire. The wheel assembly is a genuine Segway part and its size is specific to your x2 Personal Transporter’s software. The deeply treaded, all-terrain tire diameter is 21″ (53 cm) (21×7 R10) and mounts on a x2 rim. Its tread pattern and rubber compound have been specifically selected to provide traction on a variety of challenging terrain as well as a smooth ride on pavement. Segway requires that PT riders use only genuine Segway wheels and tires given that they are an integral component of your PT. Keep in mind that you may re-use fasteners when replacing a wheel.