Kickdown is a mechanism in automatic cars that allows the driver to drop a gear by using the movement of the accelerator pedal. It is a downshift in an automatic transmission triggered when the driver pushes the cars accelerator to the floor. By dropping a gear, the car is able to gain a burst of power and acceleration through increased engine revs, just as it would in a manual car. Kickdown is designed to be used whenever a driver needs to increase the immediate power delivered by the engine, such as when overtaking a vehicle or driving uphill.

Before computer control became widespread, most automatic transmissions would kick down only if the accelerator was pressed all the way to the floor. More modern transmissions may kick down, by one gear or more, earlier in the gas pedal’s range of movement, based on the pedal’s position or rate of change. Some vehicle central computers compare the current speed with the position of the accelerator, and if the vehicle is not accelerating as much as it should, the computer will signal the transmission to kick down.

In summary, kickdown is a mechanism in automatic cars that allows the driver to drop a gear by using the movement of the accelerator pedal, providing the engine with more power and acceleration through increased engine revs. It is designed to be used whenever a driver needs to increase the immediate power delivered by the engine, such as when overtaking a vehicle or driving uphill.