Double-clutching is the proper way to downshift at speed without placing excessive wear on the transmission's synchronizers. This allows you to select a much lower gear without the tell-tale lurch you normally get when the clutch is let out after downshifting.
Sample:
When downshifting from 4th gear to 2nd at 50 mph and to prevent excessive synchroniser wear, the clutch is depressed and the shifter is moved to neutral. The clutch is then released, and the gas is depressed to bring the engine speed up to where it needs to be for the lower gear. The clutch is then depressed again and the shift lever moved into the lower gear. When the clutch is released the second time, the engine is already turning the proper speed . While this sounds complicated, it's easier done than said, and only takes about a second.
This combines double-clutching and braking into one event. Place your foot on the brake as far to the right as you comfortably can. While braking, roll your ankle so you can catch the left edge of the gas pedal with the right edge of your foot. If the pedals are too wide, try placing the ball of your foot on the brake, and the heel on the gas (This is where the term heel-and-toe originally came from). Now try gently slowing down and downshifting. With practice, you can brake hard and downshift in one smooth motion. This will prevent the wheels from locking when the clutch is let out in the lower gear, and you will be ready for a burst of acceleration coming out of your favorite corner!
So really, both techniques are used for cornering? Because the way I understand double-clutching after reading what you wrote is that as if you are slowing down into a corner and you slip it out of gear, then rev the engine to a nice launch RPM out of the corner, then you put it in gear to launch yourself through the corner?
For some reason I always thought double-clutching was done whether down-shifting or up-shifting.
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Back in the day you had to double clutch because trannys didn't have syncronizing gears. So if you wanted to shift from 1st to 2nd, it would grind the gears unless you double clutched. Double clutching helps get all of the gears in the tranny moving at the same speed (now accomplished with syncro gears).
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It is not a ricer term, the term double clutching is as old as racing.
Willit said it right, was mostly used when transmissions had no syncrhos, but it is a technique still in use by some as it reduces wear on the synchros and allows you to keep your engine in the powerband.
Rally racers are an example of fellows that use double-clutching + heel and toe downshifting.
Originally posted by wilit Back in the day you had to double clutch because trannys didn't have syncronizing gears.
My late Grandfather once told me about this. He drove rigs. He used to brag that he could shift through the gears and back down again w/out using the clutch. Sounds hard as h#ll to me, though...
Yeah, double-clutching goes way back. Ricers say how they double clutch but I doubt they even know what the term is or how to truly do it. I was correct on my thinking of how double-clutching works, I was just confused by your explanation of it.
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Gasoline is for washing parts.
Alcohol is for drinking.
Nitro is for kickin ass!
1967 Mustang Coupe
R.I.P. Darrell Russell 1968-2004 The racing world has lost a great racer.
My old school bus driver used to double clutch, It was used back in the day when synchros were in even used. Alot of big rigs still do the double too. JT...
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Stupid question... Why do you have to go to neutral and release the clutch before down shifting? Could you match the RPM while you are downshifting and skip the "pause" in neutral?
Originally posted by Bama Stang Stupid question... Why do you have to go to neutral and release the clutch before down shifting? Could you match the RPM while you are downshifting and skip the "pause" in neutral?
I was wondering about this at first, but then realized its importance. The key to NOT grinding your gears is to get your transmission moving at the same speed as the engine for the future shift into a lower gear. To do this, you'll need to speed it up to match what the adjusted speed of the engine will be after down shifting (RPMs). When you let go of your clutch in neutral, your transmission will once again spin at the speed of your engine and you'll be able to speed it up at that time to what you think will be the future estimated RPMs for the gear you're shifting into. Then, you push in the clutch to shift, shift, and walla: your not really working your synchronizers if you did it correctly.... Follow?
Originally posted by GrimlokTT My late Grandfather once told me about this. He drove rigs. He used to brag that he could shift through the gears and back down again w/out using the clutch. Sounds hard as h#ll to me, though...
Not hard at all, just a little practice needed. Actually it's the easiest way to shift a big truck. And it depends on the transmission your using. Eaton's are the most forgiving, and Spicer's are the least. Also alot of new heavy service transmissions are split shifted with auto range selection, like the Eaton Super 10, and Super 10 Top 2. With these type you only physically shift once for 2 gear changes, the second shift is preformed by a spliter switch on the side of the shift handle.
You can also shift a T-5 without clutching, just like a big truck, though I don't recomend a novice try. I do it alot without thinking out of habit from the big truck, but out of habit from the big truck I've also memorized the speed to RPM to gear ratio, and how much fall is needed to upshift, and how much to rev and fall for a downshift. It has a very tight window of RPM to make the shift, like the Spicer's I've shifted about a couple hundred thousand times.
But when I racing (AuotX), I always use the heel and toe method as explained by GTRaptor with the exception I don't double clutch.
double clutching 
