Do I need special wheels for outdoors or bigger carts?

The foam-filled wheels were custom made for K-9 Carts. All but the smallest tires, have knobby tread to assist with traction outside. Wheel choice is based on the ability or strength of the pet. Large wheels are suggested for use on rough terrain. Small wheels enable the small or weaker animal to walk more easily. Occasionally we provide two different diameter wheels for optional use.