According to at least one BF thread a few years ago, 650B wheels were only used by Schwinn in 1991. As above. Go figure. I had thought that [almost] all MTBs from early 80's through just a few years ago used 559.

There was also an oddball Raleigh city bike from about the same time frame that used that tire size. Those bikes used to give us fits when they became a few years old and started needing replacement tires. That size was scarce (In the US anyway) and Schwinn was the only vendor that could get them for us. I also recall that you couldn't fit regular 26" (559) or 700C wheels on these bikes as the brakes didn't have enough adjustment to line up with either one.

I always thought it was odd that Schwinn would spec a strange size rim for a few low end bikes. The Frontier took a steel rim and the Mirada took an alloy. I can't remember but I believe the three-speed Schwinn Suburban used that size alloy wheel in 1991 too.