Dunbar, I've ridden a couple of Juiced bikes for short intervals and thought they achieved 28 mph (sometimes test bikes may be "juiced'); surprised to hear yours didn't achieve 28 mph. I'll probably order a "dongle" for my Yamaha Haibike one of these days now that its warranty has expired, but don't now what to expect (I've heard everything from 26 - 35 mph). My "1500w" (30 amp controller, 52V - $600 kit + battery) Frankenbike does 33 mph easily (on Cyber Monday they were selling the rear hub kits for $157 delivered).