Actually thats not that hard. I'm a roadie and 20+ MPH on flat ground is fairly easy. Even Ezip could be pushed hard (without the motor). But because of the gear, the limit seems to be about 18mph.

And yes, I did modified the engine/battery recently to cut down on my commute time (typically 18-20+ mph instead of 14-17mph)... Again, the problem is that I like to pedal (hard) but at that speed, the pedal is useless.

So let me know if you know the spec as I didn't find anything in the owners manual.

As for going down the hill at 50mph - I recently came back from a grueling Vermont trip and I must say - Wow!!! Coming down the mountain at 50+ MPH for few miles was excellent. Bad thing was - took us 3 1/2 hours to get up to the top and most of us chickened out and hit the brake once it began creeping up to 60mph.