The tension of your chain is very, very, very important…especially if you are riding a fixie. The tension of your bike chain is made looser or tighter by moving the rear wheel backwards or forwards. It is important to have the correct tension because if the chain is too tight, the drive train will bind and if it is too lose, the chain can fall off…and that can mean no brakes…and you don’t want to be flying down a hill with no brakes.
I really like how Sheldon Brown worded his method on how to set the correct tension in your chain…this is how he explained it on his site:
-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.