What is a Gear Ratio?

In theory, the gearbox or transmission is a simple enough mechanism; however, the building up of such a device needs to be precise and strong, and therefore can become quite complex. Getting the gear ratio right is crucial for good engine performance. Inside a gearbox are cogs/gears of different circumferences that have teeth on the outside running edge. These teeth are for meshing a driving gear into a driven gear so that the desired movement of a vehicle can be achieved. The gearbox takes the power developed from the engine and uses these series of teethed gears to give a car more power and less speed, or less power and greater speed. To achieve this, the gearbox, by use of the different gears inside the gearbox, will speed up or reduce the rotary motion of its input shaft compared with its output shaft. Using gears/cogs with differing circumferences and or a differing number of teeth allows different gear ratios to be created. A gear ratio is the number of revolutions made by a driving gear as compared to the number of revolutions made by a driven gear of a different size. So, if one gear makes three revolutions while the other gear makes one revolution the gear ratio is 3 to 1. These differing gear ratios are the essence of how a car can use its engine power as torque to accelerate, travel at speed, pass other cars and climb hills.

Without a gear box and gear ratios, driving would be exceedingly difficult and, in some situations, impossible.We hope that helps answer the question ‘What is What is a Gear Ratio?’!

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