Early manual transmissions were simple and clunky devices. Gears spun at different speeds within the transmission, making it difficult to slide them together. This problem was especially pronounced when downshifting. Between the 1940s and 1950s, automakers and engineers added ‘synchros’ to transmissions. Synchros solved the problem by synchronizing the speed of the gears, allowing drivers to shift smoothly.
Double-clutching is a form of manual synchronization that reduces grinding. The process allows the driver to manually match engine RPMs to the transmission speed, allowing gears to slide together neatly. Double clutching isn’t always necessary when shifting up, as the deceleration of the engine allows the driver to find the ‘sweet spot’ RPM without touching the throttle. However, when downshifting, the driver has to ‘blip’ the throttle to find the ideal engine speed.
How to Double-Clutch
Double clutching is the process of pressing and releasing the clutch twice while shiting. Remember, one half of the Double-clutching may be tricky at first, but it becomes muscle memory with practice. The basic process goes something like this:
1. Depress the Clutch
Before shifting, depress the clutch pedal to the floor and hold it there. This would be the ideal time to start braking if you want to slow down.
2. Shift into Neutral
With the clutch still depressed, shift the transmission into neutral. At this point, half of the transmission is synchronized with the road. When you release the clutch, the other half of the transmission will synchronize with the engine. The goal is to match these two speeds.
3. Release the Clutch
Release the clutch and keep the transmission in neutral. At this point, the transmission is synchronized with the road and the engine, but neither side is in mesh (or connected) with the other.
4. ‘Blip’ the Throttle
With the clutch still released, tap the throttle and gain some RPMs. The amount of throttle required depends on how dramatic the gear change is. Over time, you’ll get a feel for it.
5. Depress the Clutch
Immediately after tapping the throttle, depress the clutch again. The ‘engine side’ of the transmission will continue to spin but will be disconnected from power.
6. Shift into Desired Gear
Apply pressure to the gear shifter as if you’re shifting gears, but don’t force it. As the ‘engine side’ winds down, it’ll eventually reach the point when both halves spin at the same rate. Once you find the sweet spot, it’ll slide into gear easily without grinding.
7. Release the Clutch
Once the shifter slides into place, slowly release the clutch and try to find the right engine RPM to continue driving. With some practice, the whole process takes only a moment or two.
Is Double-Clutching Still Necessary?
Double-clutching is an obsolete shifting method for ancient gearboxes, and you’ll probably never need to do it in a modern car. Some heavy-duty commercial vehicles still use unsynchronized transmissions, but even 18-speed semi-trucks don’t always require it. However, double-clutching is a great way to feel-out a manual transmission and sharpen your skills. You’ll learn to rev-match and shift smoothly, boosting your confidence and improving your driving capabilities.
If you learn to find the ‘sweet spot’ in a modern car, you can try to upshift shift without using the clutch at all. Be careful when doing this, but masting these skills is a great way to impress your friends and save some leg work. But don’t shift without the clutch from a dead stop—think about it, I shouldn’t have to tell you why.