Originally Posted by
jeebusaurousrex
There was probably some crossover between model years since I have a 1987 Circuit frameset that was actually built in 1986.
During the seventies and eighties, it was common for Schwinn production for the next model year to begin in October, so a bike with a frame serial number indicating an October, November, or December manufacture would be built to the next year's model specs. For example, a 1987 model year Circuit might actually have been built during the last three months of 1986.
I don't believe Schwinn would have built a 1986 model year bike in 1987, though.