How to choose the number of teeth of large sprocket

BigSprocketsNumber of teeth = number of teeth of the small sprocket X speed ratio

After determining the number of teeth of the small sprocket, multiply it by the speed ratio, then the number of teeth of the big sprocket can be determined. Generally speaking, the number of teeth of small sprocket should be 17 teeth or more, 21 teeth at high speed, and 12 teeth at low speed, but the number of teeth of large sprocket should not exceed 120 teeth. In addition, when the speed ratio is 1 : 1 or 2 : 1, please choose the sprocket with large number of teeth as much as possible. In general, please set the speed ratio to 1 : 7 or less, preferably around 1 : 5.