I posted the description of my ideal in the "introduction" forum, and it's pasted below. I've now had a chance to look around the forum, and here's my impression: There are two approaches to motorized bicycles. One is to take advantage of the power of even a very small IC motor compared to a human "motor" by attaching it to a vehicle that is heavy and "clunky" compared to a state-of-the-art mountain bike. You have so much power to spare that having a really efficient platform isn't that important. This appears to be the most common approach seen on this site. (This approach also allows greater "personal expression" by individuals who may be just a bit - eccentric. ;-) ) The other approach is to take advantage of the inherent efficiency of the bicycle, especially a state-of-the-art one, to minimize the size, weight, fuel requirements and output of the motor. My "ideal" described below is based on this approach. This forum helped me realize that when I dreamed this up I did so with the idea of being able to "portage" the bike in an off-road or broken-road situation, such as across a stream, say. In other words, being able to pick it up and carry it almost as easily as lightweight mountain bike. Also, I was thinking in terms of retaining full mountain-bike efficiency for non-motorized operation. Actually, the context of all that is a "survivalist" situation, but the application for more prosaic and realistic scenarios is obvious. Among these would be use in undeveloped parts of the world, and off-road touring. Or just bopping around town in a low-profile fashion. So without further ado, here's my ultra-high efficiency ideal: - Virtually the same weight as a standard high-tech mountain bike that has a full suspension, except for the addition of a tiny motor, I mean like 25 CCs or less, just enough to propel the bike at around 25 mph (40 kph) on flat pavement with no headwind. - A gasoline motor like the one described above. (I picture a chainsaw or weed-whipper motor.) - Transmits the power to the front sprocket of a mountain bike derailleur, so that the small amount of power available could be used in the most efficient way possible via the 15, 18 or 21 gears available. I picture a motor mounted behind and beneath the saddle, with the chain going to the front sprocket (I think chains are very efficient, if a teensy bit heavy.) - Has fat tires like a mountain bike, but slightly optimized to give better traction on pavement for safety. (With standard mountain bike tires an option for off-road use.) - Has wheels that are almost as light as those on a high-tech mountain bike, but just a teensy bit more robust to stand up to sustained speeds on pavement that are slightly above typical pedal-bike speeds. - Has top quality mountain bike disk brakes for safety. They cost more and are a bit heavier than rim brakes, but give better, more consistent brake performance in all conditions - critical given sustained, higher-than-average speeds on pavement. - (Perhaps) has a "self sealing" gas tank for safety. This is very simple - it just means a foam liner that prevents the gas from pouring out when punctured, unless is really gets smashed. - Has full-bicycle functionality, and even allows the user to quickly remove the motor and appurtenances. This would be the ultimate 'green vehicle' for around town use. It would not be allowed on freeways, obviously, but if you didn't mind only going 25 mph you could cross a continent with it, using less than 15 gallons of gas! They could probably sell around 300 million of these in China and the third world. Except it wouldn't be cheap - it only works by using expensive high-tech materials and technologies. Still, it should be possible to make this for around $3,500, given the cost of high quality mountain bikes. A recumbent version could have all the same features. in a slightly heavier but more comfortable and aerodynamic package.