Originally Posted by Nehmo
My friction drive is a wooden roller 3.5" diameter pressed to the tire by the weight of the 79cc engine.
But since I began writing this post, I moved my gas tank to the front of the bike. The pic above is it. (It's a shot at a distance & cropped.)
This will reduce the weight even more, but I'm thinking on using a spring arrangement rather than what I have.
I believe you're going to have to apply more weight/force to the tire than you are doing.
Engine weight alone won't do it. We did some experimentation and came up with somewhere between 30 to 40 lbs to provide enough friction for wet streets. Do you have a way to adjust the roller position relative to the tire?
Also are your tires smooth or knobby?