I thought i would try one of the analog speedometers on my bike and see how it goes. As best as i can tell it reads about 10 mph fast. I base that on my FD with a Zenoah G430 and what i see on the Gear Rat . At 5500 rpms i should be going 18.41 mph. the speedometer says 28 mph. Just thought anyone else might like to know what i found out. My tech.is reading about right. I have a 1.125 dia. drive roller.