Originally Posted by
tatfiend
Depending on your location part of the magnetic material could be from the local dust. Try dragging your magnet through the dirt for 100 yards or so and see what it picks up. The results can be surprising.
Agreed, when I first got into biking, soaking my chain left at least a teaspoon of ferrous material. I, like many, assumed that this was my drivetrain disintegrating due to poor maintenance / componentry. I resolved from then on to be more regular with my maintenance. However, every time I cleaned the chain (I ALWAYS soak) I'd end up with a comparable amount of ferrous silt to the first time. However, my drivetrain appeared no worse for all the wear it should have been accruing. From then on I figured it must appear worse than it was, and just took the deposits as par for the course when cleaning. When I added full coverage fenders and "fredded" up with an extended front mud flap I noticed that when I cleaned my chain the collection of silt had reduced dramatically. Obviously, my front wheel was throwing grit onto my chain, most of which happened to be ferrous. I guess you could also make the argument that a reduction in grit on the chain would also reduce the amount of wear the drivetrain is subject to, however, I think a majority of the sediment is from the road not my bike.
EDITED:: out of respect the english teachers I've left in my wake...