Originally Posted by
Frankfast
I replaced the chainring on my single speed with one with less teeth. I tried to adjust the wheel in order to get the correct tension on the chain but while rotating the crank the chain would tighten and then loosen depending on the position of the crank. The wheel is centered and the crank seems to be on the tapered shaft of the BB correctly. Could the new chainring be out of round? Has anyone had this problem?
The correct tension for the chain is NO tension. You want the tightest position that always has some slack as the crank rotates. This is a two step process because chainrings are usually slightly (or more than slightly) eccentric, and chain tension varies with crank rotation.
Pull back the wheel until most of the slack is out. Rotate the cranks holding tension by pushing the middle of the lower loop up. (keep fingers to the outside of the loop, ie under the lower loop) and feel for the position of least slack. Keeping the crank there, pull the wheel back until there's only a vestigial amount of slack, enough that you can freely push the center of either loop up or down 1/4". Finally check by rotating cranks and watching and listening to confirm that the chain is never actually tight.