Gear Systems

Gear ratios, speed and torque

Gear Ratios and Applications

Gear systems transfer rotary motion between shafts. The gear ratio determines the trade-off between speed and torque (turning force). A small gear driving a large gear reduces speed but increases torque. A large gear driving a small one increases speed but reduces torque.

Example

Calculating Gear Ratio

Gear ratio = Number of teeth on driven gear ÷ Number of teeth on driver gear Example: Driver gear = 20 teeth, Driven gear = 60 teeth Gear ratio = 60 ÷ 20 = 3:1 Meaning: driven gear turns 3× slower but with 3× more torque Bicycle low gear: small front + big back = easy pedalling (hill climbing) Bicycle high gear: big front + small back = fast speed (flat road)

Note

Remember

You cannot increase BOTH speed and force — it's always a trade-off. Gear trains (multiple gears in series) can achieve large ratios. Idler gears change direction without changing the ratio. Worm gears provide very high ratios and prevent reverse motion.

Key Vocabulary

Gear ratioThe relationship between driver and driven gear sizes

TorqueRotational force (turning power)

Driver gearThe gear that provides the input motion

Driven gearThe gear that receives motion from the driver

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Gear ratio

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