A chain drive system has a driver sprocket with 24 teeth and a driven sprocket with 72 teeth. If the driver shaft has 633 ft-lbs torque, the torque on the driven shaft will be __________.

• A. 1899 ft-lbs
• B. 633 ft-lbs
• C. 1266 ft-lbs
• D. 453 ft-lbs

Answer: (A)

When a smaller driver sprocket with 24 teeth drives a larger driven sprocket with 72 teeth, the output speed drops while the output torque increases in proportion to the teeth ratio. Since power remains roughly the same in an ideal chain drive, the torque scales by the factor of the driven-to-driver teeth count: 72/24 = 3. So the driven shaft torque is 633 ft-lbs × 3 = 1899 ft-lbs. In real life, some losses would slightly reduce this, but the ideal calculation gives 1899 ft-lbs.