No, its not variable ratio. There is a fixed geometric relationship between the diameter of the driven wheel and the pitch circle of the rollers on the spider. Tel--Good to hear from you.--I am constantly on the lookout for ANYTHING that has a "neat" mechanical movement about it, that can be driven with one of my engines. Its hard to imagine, but there simply aren't that many things that are "quick and easy" to build, but pleasing to see run.---Brian