"I can't tell you what works best but I can assure you that tires like the Maxxis Hookworm with a wrap around tread are far from ideal. I had to machine a wheel of vulcanized rubber and adhere it to the metal contact wheel on the bottle generator. It's larger diameter dealt with the tread much better and also reduced the tire diameter/generator ratio to reduce the drag a little and keep the voltage of the generator down to acceptable levels when running 406s at speed. I run DIY LED head/tail lights so I also had to include an ICVR (http://www.radioshack.com/product/in...ductId=2062599) (up to 35v in, 5v out), just in case, to keep my LEDs from burning out. Keep in mind that bottle generators are normally intended for use on larger wheels."

I believe that a bottle generators input and output are affected by angular speed / rpm as it is the sidewall that drives the generator and if that sidewall is passing at 168 rpm on a 20 inch wheel and 135 rpm on a 622 at the same linear speed of 10 mph that this does affect the input and output.

In practice it just means that a small wheel will deliver power differently than a larger wheel at the same speed... after you get up to a normal speed the output should be pretty much the same and then at higher speeds one might have to worry about lesser generators over-powering the lights and possibly burning them out.

I have not done any scientific testing but have observed that bottle generators on smaller wheels do seem to light up more brightly on smaller sized wheels at slightly lower speeds and like you found that they do seem to come with more drag.

The same thing happens when you use a standard hub generator on a smaller wheel and why Son makes a hub generator for 20 inch and smaller wheels that does not work properly with larger wheels due to low speed voltage issues.