It is an amazing little motor for what it is, we have gotten 45 mph out of it with the right tire.
With that said, I would actually slow it down to 41.5 mph top speed due to heat build up by using a SMALLER tire on the motor.
We have fielded dozens of bikes based on that motor controller in 48 and 60 volt versions, they are all used daily as dependable alternative transportation for folks and we have had ZERO problems, but we set them up for them, made sure the shifters were aligned and functioning properly, replaced the cheap thin rubber soft china tires with stiff rubber smaller Michelins.
That motor winding and shift design is unique in the industry, and it is STILL used today around the world, it is extremely inexpensive to produce and provides, via the shifter, two completely dirrent motor winding types, one for torque, one for speed.
That motor design is owned exclusively by Amoyee Chen of EFUN and is still offered on their line of bikes if one desires it, although most opt now for their 6 phase systems. But some importers still order this motor as there laws are much strictrer and they are not allowed to use the more powerful 6 phase offerings.
You can get 60 miles in low speed mode (22mph) on level ground using that motor and GreenSaver SP27-12 bats, I have done it several times.
The stock controller runs around 46 amps, but using a cycle analyst can be limite to 38 amp and the reduction in loss from Puekert effect on the batteries from this reduced amp load can greatly increase range without reducing top speed, although accel is effected a little as is hill climb.
Do not over heat motor or large power wires may desolder, the China solder on the power wires was not always that good, all of ours are resoldered prior to sale.
Do NOT shift the cup back and forth out of boredom, it flexes the wires and they can work break loose, same when very cold out, try not to shift a lot as the cold stiff wires will tend more to stress and may come loose.
PS go to
http://en.wikipedia.org/wiki/Brushless_DC_motor
and look at the image for delta and wye windings
I think this is what the shifter is doing, changing between delta and wye windings, but I am an idiot, what do I know ?