Double clutching is a gear-changing technique for some manual transmission cars. For newer cars of today, most are built with synchronized manual transmission systems and only require a single clutch technique to change between gears. In the case of older vehicles for example, some require the double clutching technique which basically adds one more step to be able to shift from one gear to another. The extra step basically involves depressing the clutch pedal for the second time in the whole technique hence it is termed as double clutching.
For single clutching using new cars, one will simply depress the clutch pedal to shift gears. Changing gears from first to second for example can simply be done with a single push of the clutch pedal. In other cars, before one can shift from one gear to another, the clutch must be disengaged from the engine first before it can be shifted to another gear. This means that the gear must be put in neutral first before proceeding to shift to another gear. This process basically requires pushing on the clutch pedal twice. The first is during the shift to neutral and the second is during the shift from neutral to the desired gear. This double clutching process also requires that the engine revolution is synched with the appropriate gear. Only when the engine reaches the appropriate or desired speed can the driver shift the gear from neutral.
The double clutching technique is not common for new car models of today although some trucks and other vehicles are still configured for this specific clutching technique in terms of gear change. Racing cars are also typically setup for double clutching as this technique significantly reduces the wear and tear of the clutch components. This is especially beneficial for cars that are used frequently like race cars and some trucks.