# There is 1 thing I just don't get about "double-clutching"



## MomoB12 (Jul 22, 2003)

From wikipedia:



> However, in order to downshift, engine RPMs must be increased while the gearbox is in neutral and the clutch is engaged. This requires the driver to shift into neutral, *release the clutch pedal*, apply throttle to bring the RPMs up to a suitable speed, depress the clutch pedal again, and finally shift into gear.


Really, by releasing the clutch pedal, any engine loses it's load and therefore lowers it's RPMs, so I don't see any need for actually putting the gearbox in neutral. Don't you just, let's say, depress the clutch, move the gear from 4th to 3rd, and before releasing the clutch, rev your engine to your desired speed? 

Or, depress the clutch, move your gear from 3rd to 4th and then just release the clutch? Really, how is putting the gear box in neutral and releasing the clutch going to make my engine lose RPMs any faster than having the clutch depressed? The engine is still disengaged either way.

Or someone enlighten me.


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## Matt93SE (Sep 17, 2003)

Why do you think you need to double clutch? because Vin Diesel mentioned it in fast and furriest?


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## MomoB12 (Jul 22, 2003)

Matt93SE said:


> Why do you think you need to double clutch? because Vin Diesel mentioned it in fast and furriest?


Yes, I do remember him saying it in maybe the first movie, but I don't think I need to double clutch at all. I've seen professional drivers do it and I don't really see the point. Are you going to give anything to the thread or just try to look cool?

Look it up in Youtube, you'll see some professional drivers doing it (And I still don't see what's the use)


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## Matt93SE (Sep 17, 2003)

professional racers do it on a DOWNshift. your question states it as an upshift and downshift. It's completely unnecessary for anything but a non-synchro semi transmission on an upshift and still not necessary for a synchro tranny on a downshift.

when downshifting, you do it to match the speeds of the shafts and gears in the transmission to the engine and driveline speeds before engaging gears. this is especially important in non-synchro transmissions used in racing. not so important in a synchro tranny like what you have in your street car.
often what I'll do on the track is simply pull the tranny out of gear, blip the throttle to rev match, then slip it into the lower gear. done right, I don't even use the clutch...

Also, if you'd do just a bit of reading, you'll find the info has already been discussed in great detail.
found this on page 2 while I was browsing for another topic... http://www.nissanforums.com/motorsports/101347-poll-double-clutch-heel-toe-normal-heel-toe.html


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## MomoB12 (Jul 22, 2003)

Matt93SE said:


> often what I'll do on the track is simply pull the tranny out of gear, blip the throttle to rev match, then slip it into the lower gear. done right, I don't even use the clutch...


Thanks, but that's the thing I don't get: Will releasing the clutch while the gears are in neutral do anything different than just keeping the clutch pressed on ANY gear? 

And yes, I am totally aware that people who know their tranny so well can downshift without pressing down on the clutch, it's really common on semi-truck drivers. That's why I still don't see a point in double-clutching.


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## Rob E (Dec 18, 2005)

The reason that you let out the clutch and then rev the engine slightly is to reduce wear on the synchros, and get the engine revs to match the revs that they will need in the lower gear. Much like your example of the diesel truck driver shifting down without using the clutch, matching the revs to allow the next gear range down to be engaged. Think about it as just pushing the gear lever into neutral while you let off of the gas and revving the engine slightly to increase the speed of the transmission internals, then push the clutch in to select the next lower gear. When road racing this allows you to let the clutch out in that lower gear without worry of losing traction the drive wheels. On rear wheel drive V-8 cars with alot of compression not matching the revs can be a big problem and lock a wheel. On front-drive 4-cylinder cars it is less likely to upset the balance of the car by just selecting the next lower gear and letting the clutch out. It will wear the clutch a little bit, whereas properly double clutching will reduce clutch wear and extend synchro life.


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