Today I did 18.62 miles and the voltage was down to fluctuating between 35 and 34 volts and the speed was 14 to 15 mph. I do peddle along most of the time but not with too much pressure. I need the exercise because I weigh a little more than 240. So far the bike hasn't broke in half from too much weight.
I don't recommend using a Bike Friday for an electric conversion, it is just one of the bikes that I had in the garage that I thought would make a good first electric conversion project. Bike Fridays are made here in Eugene, one of these days I am going to ride by and let them take a look at it to see what they think.
I have a recumbent which will be my second project. I am still ordering parts for that one.