The belt drive ratio is directly proportional to the drive ratio. Which statement best completes this relation?

• A. Inversely proportional
• B. Not related
• C. Directly proportional
• D. Exponentially related

Answer: (C)

The main idea is that both quantities are governed by the same pulley size ratio. The belt drive ratio is defined by how much larger the driven pulley is compared with the driving pulley (the diameters ratio). The drive ratio used in this context is a corresponding ratio determined by the same pulley size relationship. Because they rely on exactly the same geometric ratio, changing the pulley size ratio scales both quantities by the same factor. In other words, if you increase the diameter ratio, the belt drive ratio increases in direct proportion to it. For an ideal belt system, doubling the diameter ratio would double the belt drive ratio as well. That’s why this is described as directly proportional. In real systems, small losses like slip or elasticity can tweak the numbers slightly, but the linear, proportional connection remains the core idea.