Chain tension is a very debated area and often filled with contention. Owners manuals provide reference points or recommendations but leaving the chain too tight causes a myriad of problems that can create extremely significant and ultimately expensive repairs!
You need at least 1.25 inches of free play in a chain if your suspension has 4.5 to 5 inches of travel. Failure to ensure this means that when the shock reaches a certain point in its travel, the chain binds/tightens and tries to stop the shock from moving any further. That can lead to wheel hop, loss of tire grip on the road or worse, severe stress on the countershaft bearing shaft. Engine cases are very light given the weight saving competition we have between manufacturers, so a tight chain will try to pull that bearing back in the engine cases towards the rear wheel to create chain slack.
Clean, lube and adjust your chain every 500 miles and it will last over 20,000 miles easily provided your rear wheel is aligned properly!
Bad chain tension? too tight!
Let’s take a look at OnTheThrottle’s video using a 2009 Yamaha R6: setting chain tension correctly