I use Mr. Clean Erasers to get caked on road tar and baked on bug juice off my pipes, wheels and chrome covers. Be very patient, persistent, don't press too hard and don't use on frame or painted surfaces. Much, much finer than steel wool, almost like a baking soda type consistency, I bought a box just for the garage after using up all of the wife's kitchen supply. Works great.
For stubborn stains I dab Easy-Off oven cleaner on with a rag as to avoid overspray and let soak overnight, then hit it with the eraser.
Edit: I just came in from washing the bike, I tried a little more force with the Mr. Clean Magic Erasers on the pipes, no worries.
