Can anybody tell me what this black stuff is on my rear wheel (pics below)? For what it's worth, I'm still pretty new to bikes in general, and I've only owned this one a few months (it's a 1999 R1100S +ABS with ~35,000 miles).
It's mostly on the drive-side of the wheel and it seems to appear after I take a long trip (~150 miles with very few stops). If I clean the wheel up and take a bunch of short rides, like 20 miles back and forth to work, I don't see much, if anything, on the wheel... It's really only noticeable after a single long trip.
I changed the rear drive fluid the day before I took my last ~150 mile trip, so if that's what was leaking, I don't think it would be as black as what I'm seeing. It doesn't really feel like oil either... There's not enough of it there to get a good "feel" of it, but it doesn't seem to be as runny as oil.
It looks like it could be originating where the wheel meets the final drive, but it's really hard to get a good look in there without taking the wheel off (which I have not done yet).
Could it be rear brake dust collecting and then just flinging out to the outer-rim of the wheel? If not, what else could it be?
(Sorry about the picture quality -- I had to take them with my camera-phone.)
Thanks!
