Dwanecart was designed my two aeronautical engineers, one of which had a German Shepherd "Dwane" who needed assistance.  The very first prototype of the chair was made in 2005 out of an steel lounge chair and the tubing was bent on the back of a car bumper. They designed the cart with a swing axle plate which is like a  Roman chariot design.

The design puts the  placement of the weight of the dog on his or her's  front legs. There is  no need for a neck strap: We reluctantly recommend adding one only  if a dog is too weak to lift the 1-2 lb weight transfer onto the front legs (on the Large & Mid-Sized Dog).

The 12" or 20"  BMX tires provide ample suspension, ride through most terrain, and they are also tall enough with the attaching plates to keep the dogs feet from dragging on the ground, hence no boot straps.  After the passing of Dwane they decided to put he cart on Ebay and so the design has evolved into steel welded construction, lazer cut plates and is actually bend on a tube bender instead of a car bumper.