I wonder how long it takes a finger nail to grow back. I had my bike up on the jack this morning and cleaning the rear rim and spokes. I got to spinning the wheel and looking at the clearance, since I am thinking about a 180 tire. The next thing I know the small rag I was holding goes into the rear sprocket and my finger along with it. I iced it down with a bag of frozen veggies and then had to drill with a needle to get the pressure off, but I know the nail will be history. It would have been a lot worse if i had done that with chain drive. Sometimes I feel really stupid.