Shift time

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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. Shift time is measured by the time it takes for the engine rpm to synchronize with the next gear input speed target. This is illustrated by ZF, describing the 100-300 millisecond shifts of their DCT transmissions.^[1]

Reducing shift time is important in performance and racing vehicles because upshifting 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 execute fast gear changes. Historically, a dual-clutch transmission 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 and transfer torque from one clutch to the next clutch with the pre-selected next gear, thus reducing shift times. Standard planetary automatic transmissions have caught up to DCT transmission shift times by also utilizing clutch to clutch shifts. For older transmissions, 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.

With a manual transmission, upshift time can be reduced by installing a lighter flywheel. During an upshift, the engine speed must decrease to synchronize with a higher gear; a lighter flywheel will allow the engine speed to drop more quickly, leading to shorter shift times.