In brief, FXR's debuted in 1982 as the Superglide II. They continued in 1983 and then got the EVO engine in 1984 and continued in that form until they were discontinued in 1994. The frame design was derived from the XR racing frames of the day, meaning lighter and stiffer than the previous big twin frames. They also got rubber mounted engines. Some Harley diehards were offended by the visible frame members and side covers, saying that it reminded them of japanese bikes, but the lighter weight and handling characteristics, combined with the EVO and rummber mounts made for a Harley with great handling and acceleration. In 1982 Cycle World tested an FXR at 14.26 in the quarter and 99 MPH in a flying half mile.
In 1991 FXR's were still being made but Harley brought out a new frame design called the FXDB Sturgis and it soon developed into a line all its own, replacing the FXR frame in 1995. The FXR's weren't selling as well as anticipated and the Sturgis was well received. The low sales of them while new coupled with the discovery of what good bikes they really are make them not so commonly found on the used market today.
There are still those both in and out of HD that think that the FXR was the best thing Harley ever made. As I was trying to decide what Harley I wanted I read up on all the models and was wishing that they still made them. I am a former british bike fan and loved the handling of my Triumph Trident. My FXR2 reminds me a lot of it--great handling but stable as a freight train on the highway ( and a whole bunch more trouble free). I lucked across my FXR2 on consignment at a local shop. Pristine condition.
When the CVO was opened in in York, PA. 1999, the FXR tooling was still around and HD realized that the newly introduced TC 88 wouldn't fit into the FXR frrame without substantial rework. Knowing that the FXR still had plenty of fans both in and out of the Motor Company, they decided to use it as the first thing from the CVO. The made 900 of each color of the FXR2 and 3 in 1999 and another 900 of each color FXR4 in 2000.
Any more and I'd be plagiarizing books but I hope that helps.