In a chain drive, which factor directly determines the speed ratio?

• A. Chain pitch
• B. Sprocket bore diameter
• C. Teeth count between sprockets
• D. Chain length

Answer: (C)

The speed ratio in a chain drive is determined by the relative sizes of the two sprockets, specifically how many teeth each sprocket has. Because the chain moves at the same linear speed, the angular speeds adjust according to the tooth counts: the driven sprocket’s rpm equals the driver’s rpm multiplied by the ratio of the driver’s teeth to the driven’s teeth. This means a larger driven sprocket compared to the driver slows the driven shaft, while a larger driver relative to the driven speeds the driven shaft up.

Chain pitch, bore diameter, and chain length don’t set the speed ratio. Pitch affects compatibility and strength, bore diameter is just a mounting size, and chain length affects spacing and tension rather than the gear ratio.