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Shift time refers to the time interval between gear changes in a transmission. This interval is the time in which power delivery is transferred to the next selected gear and engine speed is reduced or increased to synchronize the speed of the next gear. Shift time is usually in reference to motor vehicles but can apply to any gearbox. Reducing shift time is important in performance vehicles or race cars because the shifting process generally interrupts power delivery to the wheels. Shift time in a manual gearbox is dependent on the driver, but in automatic or automated manual cars the electronic or hydraulic control system must be calibrated and tuned to deliver a fast gear change.
Generally, a dual-clutch transmission automatic shifts faster than a standard hydraulic automatic transmission with a torque converter, or a single-clutch automated manual transmission. This is possible because the DCT can pre-select the next gear change and switch between two separate clutches to the next pre-determined gear, thus reducing shift times. Using a freewheel may reduce shift time as it may not be necessary to use the clutch. A shift kit is also intended to reduce the shift time of a manual vehicle.
In a manual transmission car, shift time for upshifts can be reduced by installing a lighter flywheel. During an up-shift the engine speed must fall for the same vehicle speed; a lighter flywheel will allow the engine speed to drop more quickly when it is unloaded leading to shorter shift times.