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Chain tightness(4 posts)

Chain tightnessspeedisgood
Jan 15, 2003 6:03 PM
How much tension do I need to put on the chain when I'm tightening the rear wheel? Do I want a little floppiness so I can jiggle the cranks a few millimeters? As tight as possible? Thanks for the help!
re: Chain tightnessfixedgearhead
Jan 15, 2003 7:36 PM
you should be able to see about 1/2 inch or so at the middle of the chain span. Too much and the chain will fall off, to tight and you will fry your bearings.

Sheldon Brown says...Tig
Jan 15, 2003 7:58 PM
Ideally, a singlespeed should have a frame with horizontal dropouts or track-style horizontal fork ends.
With this type of frame, the chain tension is regulated by moving the rear axle back and forth in the fork ends. If the chain is too tight, the drive train will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding. If the chain is too loose, it can fall off, usually at the most inconvenient possible time.

Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.

This takes a little bit of your hands learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.

Once you have the chainrings centered and secured, adjust the position of the rear axle to make the chain as nearly tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible.

I just adjust the rear wheel so that the chain tension isn't so tight it binds when the crank is rotating, nor so loose that there is more than 1/2" sag when looking from the side. You should be able to move the chain (upper section above the chain stay) up and down about 1/2" to 3/4" with your fingers. Rotate the crank about 60-90 degrees, stop the movement and "finger lift" measure it again. Do it again until the crank has completed a rotation. The chain should be fairly close in range of lift all the way around. If not, use Sheldon's method above.
A little jiggleGinz
Jan 16, 2003 4:20 PM
I think you'll find that if the chain is so tight, that the cranks have no "play" or "jiggle" in them, you are on the verge of too tight.

I'd say, go anywhere from a tiny bit of jiggle to a little teeny bit of jiggle.