How To Set Chain Slack Adjustment – Setting Correct Chain Tension

How many different ways have you heard people use to check the chain adjustment on their bike? Seems to me there are almost as many ways as there are riders. Well maybe not quite that many but it sure seems that way. My favorite is the four fingers between the chain and the swing arm. I have seen people use this technique with the bike on and off the stand. Have you ever wondered how these folks came to this technique? What great wise man disseminated this misinformation? While using this approach may give you consistent results, it is very likely giving you an incorrect tension.

Proper chain tension is determined by a relatively simple mathematical equation, 1-3% of the distance between the two axles, in this case the counter shaft and the rear axle. Say you measure these points on your bike and get a measurement of 24 inches, the equation 24x.01=.24 and 24X.03=.72 the result is a total up and down play of .24 – .72 inches when the chain is at its tightest point.

Now to get the chain to its tightest point, you do this by lining up your counter shaft, rear axle and swing arm pivot.

The easiest way to do this is by removing a few parts to allow the swing arm to move without the tension of the rear shock. Put the bike onto a stand on a level floor. You will need to remove the subframe and the rear shock unit. Laurie shows us how it’s done.

Once you have the shock out use a tie down attached to the ceiling to raise the rear wheel into a position where the three axles are in alignment.

At this point your chain is at its tightest point. This is where you will be making your measurement. Here is where things get a little tricky. The measurement we came up with using our equation is the total up and down movement. We are going to be checking movement in only one direction, up. So we need to divide this number by half, thus .24 becomes .12 and .72 becomes .36 inches of chain movement in one direction.

Find the middle point of your chain between the counter shaft and the rear axle. It is usually right where the chain slider ends but use a ruler to be correct. Place a ruler against the swing arm and while pulling the chain up at the same point, measure the amount of movement in one direction.

Using your axle blocks, adjust the chain so you get .36 inches of movement. This is the loosest your chain should be at this point. Using the same method, adjust so the chain has .12 inch of movement. If you have a chain alignment tool align your axle and tighten to spec.

With shock on put bike on a stand and measure the distance between the swing arm and the inside of the chain, this is your correct amount of free play. Add .37 inches to that amount and you have the too loose measurement. Now make a measurement insert to use for checking chain freeplay when the bike is on a stand.

Keep this in your tool box and checking your chain tension is a snap! If you use this method each time you get a new bike, you will always know your chain is in the correct tension range.

Click here for a large image of EDM shop girl Laurie