Originally Posted by
Scott Bontz
FB, I can move the upper run of chain up and down about 1/2 inch, more than the 1/4 inch sag you mention. But maybe you mean simply hangs down by its own weight 1/4 inch. But I think that would translate into going up and down a total of 1/2 inch. I'll put a yardstick across the sprockets and see how far the chain actually sags without me pushing it. And though DiabloScott appears with me on avoiding too much slack and slop, I'll try living with a little more of it and see what happens.
The guideline is 1/4" sag, or 1/2" total up and down (1/4" in each direction). But you can go tighter than that if you want to reduce the backlash.
Slack is slack so as long as there's some slack at the tightest place, found by rotating the cranks a number of times.
Note, that both the front and rear sprockets may be eccentric, so you need to go a few times to ensure that you've confirmed slack at the tightest place which will be when both high spots are opposite each other.
My track bike has very round, non-eccentric sprockets, so I've minimized the backlash by having only about 1/16" sag at the tightest place, but every drive train is different so be cautious as you try to minimize the slack.
You can also use your ears to check if the bike is in a stand. If you don't have enough slack and the chain goes taut at any point, the sound will change and you'll both hear and feel the vibration change.