How is the drive ratio of a roller chain drive calculated and what is the maximum recommended single reduction?
The drive ratio is a function of the number of teeth on the large sprocket divided by the number of teeth on the smaller sprocket, not the sprockets’ diameters. The maximum recommended ratio for a single reduction is 7:1. In practice, the practical single reduction limit is affected by; the minimum size of the small sprocket, the maximum size of the large sprocket, and the need for sufficient wrap on the small sprocket. For ratios larger than 7:1 a double reduction is preferred.
