MEASURE THE TENSION
The ideal range of movement
Find the tightest point (the least distance from bottom chain to swingarm) and take readings here. Push the chain up and down to measure the movement. The allowable range will be specified in the manual. Get someone to do this with you on the bike, as suspension compression will affect the result. It’s better to be slightly loose than tight. Moving the wheel away from the gearbox increases chain tension and vice versa.