Best Friend Mobility Quad 4 Four Wheel Full Support Pet Dog Wheelchair Cart Because sometimes all four legs and paws need a little extra help. The only information you truly need to get the right size Best Friend Mobility wheelchair is the measurement from the floor to your pets backat its hindquarters. Its that simple! Best Friend Mobility makes the easiest carts to measure for - you only need one measurement to determine what size your pet needs! If your pet has very little or no rear-limb strength, one person can be the support while the other does the measuring. Measuring your pet to determine which size Best Friend Mobility wheelchair will best fit is the quickest and easiest thing.