Yep, did some digging. According to Willie G. (in his book ' Hundred Years of Harley-Davidson') he designated the first Nighttrain in 1999 as the FXSTB for the 'Black' Nighttrain. So it sounds like the B was meant to mean 'Black' Nighttrain because he mentioned 'black' over and over....lol.

FX was first introduced in 1971, and yes it was the Superglide. According to the book, he named it the 'FX' for 'factory experimental'. And he says the 'FX' was expected to be in the line for a long time. Wiki says the 'FX' acronym means 'F' "...to denote an FL frame with XL forks...." http://en.wikipedia.org/wiki/Harley-...on_Super_Glide but I tend to believe what Willie said in his book. He does mention he "put a Sportster front fork and front-wheel assy on the Big Twin chassis" but he specifically says why he gave it the 'FX' acronym.

 

Thanks for posting this info.