Double clutching is a driving technique used primarily for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. It involves using the clutch pedal twice during a single shift between gears. The technique was required before the introduction of transmission synchronizers in the 1920s to prevent damage to an automobiles gearing during shifts. However, due to the difficulty and most often unnecessary redundancy involved in the technique, coupled with the advent of synchronized gearing systems, it has largely fallen into disuse in light vehicles.
Double clutching can be difficult to master, as it requires the driver to gauge the speed of the vehicle and throttle to the intended gear accurately; vehicle weight and road gradient are important factors as they influence the vehicle's acceleration or deceleration during the shift. The primary purpose of double-clutching is smooth downshifting to accelerate and to take care of the wear and tear of certain transmission. If you drive a modern vehicle, there’s virtually no reason you will ever need to double clutch.
