I agree Wolfgang. In order to use them, you need short swing axles on a Spyder.
Since I have them, I'll confirm that the extra inch on the 5.5" is to the outside.
I believe most of the rear brakes are zero offset, it's the fronts that WILL widen the track. Every. Single. One.
Which is why a 2" narrowed beam is needed with most discs, at least on a Spyder. The Speedster appears to have more room in the front compared to a Spyder.