Numerical values of gear ratios
The gear ratio is the ratio of the speed of rotation of the gearbox input shaft to the speed of rotation of the output shaft. A lower gear ratio indicates a higher gear, which provides higher speed and less torque. A higher gear ratio indicates a lower gear, which provides lower speed and more torque.
Here are examples of gear ratios used in various automatic transmission gears:
Forward gears
* First gear: 2.5:1 – 4:1
* Second gear: 1.5:1 – 2.5:1
* Third gear: 1:1 – 1.5:1
* Fourth gear: 0.75:1 – 1:1
* Fifth gear: 0.65:1 – 0.9:1
* Sixth gear: 0.55:1 – 0.8:1
* Seventh gear: 0.45:1 – 0.7:1
* Eighth gear: 0.35:1 – 0.6:1
Reverse gear
* Reverse: 2.5:1 – 4:1
Effect of Gear Ratio on Performance
Gear ratio has a significant impact on vehicle performance:
*Acceleration: Lower gear ratios provide sharper acceleration because the engine can spin at a higher speed, producing more torque.
*Top Speed: Higher gear ratios allow the vehicle to achieve higher top speeds because they reduce engine speed and reduce drag.
* Fuel Economy: Higher gear ratios improve fuel economy at high speeds because the engine can run at lower speeds, burning less fuel.
* Towing: Lower gear ratios are necessary for towing heavy loads as they provide more torque to overcome the additional drag.
Selecting the optimal gear ratio
The optimal gear ratios for a particular vehicle depend on a number of factors, including:
* Motor size and power
* Vehicle weight and aerodynamic drag
* Intended type of use (urban, suburban, towing)
Car manufacturers carefully select gear ratios to optimize performance, fuel economy and handling for different models.