Boom tube on our Zona is 25 inches (63.5cm) measured from center of front BB to center of rear BB.
Wheelbase is a short 63.5 inches. Stoker Kay has shrunk in the past decade from 4'10.5" to current 4'8". Tandem still fits her still perfect by lowering seat post a bit and small adjustable stoker stem movement.
Pedal on!
Rudy and Kay/zonatandem