20mph is really fast on a bicycle. I mean, it is really fast. The brakes are good but like when you buy a Porsche or Ferrari, probably 20% of your purchase goes into the engineering of braking. The cargo bike since it is heavier, if you get going too fast, you might get jacked up trying to stop on a dime. 20mph seems plenty fast for me and I foresee myself averaging 15mph in a peddle-assist mode.