1. To determine the best size for a new chain, first find the diameter of the sprocket. The distance between the sprocket teeth should equal one quarter of the diameter of the sprocket. A common error is measuring the sprocket diameter directly off the chain without knowing its distance from the sprocket. To determine the bar length, measure from the front tooth on the sprocket to the back tooth on the chain. Make sure to use a chain gauge to ensure your measurement is accurate. For example, if the diameter of the sprocket is 30mm ( 2.18 inches) and you want to make a 10/16 chain, you need to measure the chain about