Double clutching is a method for downshifting that gives you smoother transitions and lowers the wear on your transmission. It’ll prolong your transmissions life and giving you an overall smoother ride. You will, of course, need a manual transmission.
Double-clutching is usually only used by truck drivers or race-car drivers, but if you have a manual transmission, you can double-clutch. It’s easy.
Usually with a manual trans, you depress the clutch, put the shifter in the next gear, and release the clutch. Double clutching adds another step. Instead of going from one gear right to another gear, you stop in neutral and release the clutch momentarily and tap the gas. Doing this allows the engine to speed up a bit so the transition into the next gear goes more smoothly. It only takes a split second to get the gear speeds matched, so it’s all done as a nice fluid movement. So it goes like this: you want to change gears > press clutch > shift to neutral > release clutch > tap the gas > press clutch again > shift to next gear > release clutch. Done and done.
Here’s a video showing how it’s done:
There is a debate about double-clutching though, since most modern cars have a device called a synchronizer that helps match the speed of the gearbox with that of the engine. Some people say this eliminates the need for double-clutching. Still, double-clutching usually makes for a smoother ride and puts less stress on the gearbox. Either way, it’s an easy skill to learn and it’s good to know.