different types of Fats?
Well, this is a big question to answer. IIRC, this topic was covered at some time in the past in this forum or another. You can also check Fatfans.de and FirstFlightbikes.com for lots of good info. There are also scans of some of the catlogs posted on a great site (?).
Off the cuff, here is a short (probably flawed) short history. I would need to check my info at home to verify some of the dates.
82-91? Fat Chance, the original bike. Horizontal top tube, cables under BB, press-in BB bearings. There were also other early bikes such as the Kicker, but they are not too common. Earliest bikes had a "box crown" fork, available as an option on later bikes. Very cool fork, but the unicrown forks are much more common. These feel a bit dated to me due to the slack angles.
87-91? Wicked Fat Chance, same bike with steeper head tube. Later upgraded to a Wicked Lite in 92?. (same geometry, lighter tubes, top tube cables, "normal BB). There were also variations throughout these years such as the Team Comp, likewise not too common (but very nice).
I feel that steeper angles make these bikes feel more modern.
89-2000 YO Eddy, Sloped top tube, top tube cables, normal BB. Their team "race" bike, changed tubing a bit over the years. Introduced with the very cool Yo Eddy fork (later replaced by the Big One Inch fork).
Probably their most popular bike, justifiably so.
88?-93 Monster Fat Their attempt at hitting a lower price point. The first year was merely a re-badged Wicked (different decals). Later models had the same geometry as a Yo but with a less expensive monostay rear end. Also less expensive (heavier) tubing. Came with a Tange fork instead of a Fat fork. Replaced in later years by a Buck Shaver and a Bro Eddy, very similar to the Monster. A great way to get the Yo geometry for less.
The Ti Fat came out in the early 90s, same geometry as the YO. The early models has externally butted tubes. Made up until the end in 2000. Great bikes.
The 10th Anniversary model was only made in 92, has a Big One Inch fork, special tubing, one paint job. Too beautiful to ride.
A Yo Betty was made available in the 90s too, (girls sizing), available in steel or Ti. Let's hear it for the girls.
They started making road bikes with the Slim Chance in the early 90s, later replaced by the Chris Chance road and Ti bikes. They also made a Chris Cross cross bike in the late 90s.
One of the biggest changes came when Fat City was aquired by a holding company and moved from Somerville MA to South Glen Falls NY in about 94/95? After this time the bikes were made by the people at Serotta.
Some people have very strong opinions about the non-Mass bikes. All nice bikes, but are they true Fats? I'll leave that up to you.
I have really only scratched the surface, they are other folks on this forum that know a lot more about Fats than I do (although I am a big fan). If you want to learn about them, you have come to the right place (thanks to Doug).
let me know if I can help.
rick