Originally Posted by JohnDThompson

I like to be able to move the upper run of the chain up/down by about 1-2cm at the midpoint between the crank and the rear sprocket. Looser than that, and I get annoying lash when I change pedal cadence. Tighter than that, and bearings will wear quickly. It's important to check this slack for the entire rotation of the crank, as chainrings (particularly inexpensive ones) are not necessarily perfectly round. You may get it perfectly set in one position, but rotate the crank some, and it becomes excessively tight. Set it so you get the 1-2cm slack at the tightest point in the crank rotation.