Forgive me in advance if this is a major newbie question, but I've only recently started doing my own tire swaps on my 959. After removing the rear wheel, I noticed the sprocket was moving on the wheel. I was able to wobble it side to side easily by hand. With very little effort, it popped right out of the wheel. I'm talking about the sprocket and the piece the sprocket is bolted to. From the look of it, that's the way it's supposed to be but I'd like to hear(read) it from someone who definitely knows.