They do go as advertised. You have to take into effect your weight, the bikes weight, the bikes style, the type of tires, wind, terrain, all things come into any resistance on your bike. I have a 48 volt system and I get 20 mile at an average at full throttle (25+ mph). That is right what they say for my weight it is good. If you weigh 120 you will get farther and faster but, I am 190 lbs. (88 kg) and that is my experience so far and that is just after a new battery and experimenting with tires right now and having to make sure my dual disk brakes are adjusted just right every couple of weeks or so. Like I said; Every little thing makes a difference in the distance and speed you will get and the biggest thing is this is not a motorcycle and you only are going to get up to speed so fast. Believe me, it it a whole lot faster than you could ever peddle.
Check out the post under
http://goldenmotor.com/SMF/index.php?topic=2095.0 here you can find out a few things not only my getting a new battery replacement.
Don