I've only just done over 1000 km on the bike and notice when cleaning the back wheel is covered in black dust. It's similar to the Burgman Scooter I ride. Is this from the brake pads? I know I use the back brake a lot on the scooter but not much at all on the Stryker. Could the dust be from the belt? It's the first belt drive I have ever owned. I'm still amazed that the belt can cope with the stresses it is subjected to.