Is double clutching a good idea?

Double clutching serves no benefit. All it will do is wear the clutch more....

 

I will presume. Done correctly, it MIGHT offer decreased wear to the synchros at the expense of a little more wear to the clutch. Done incorrectly, it will make your synchromesh transmission seem like it is not synchronized.

I would suggest a practice session on a car with a non-synchro box to validate your technique.

 

I think so...

Joe
www,joesackey.com

 

Seems like you already know the answer to your own question.

 

I can explicitly and most definately say that your theory is indeed correct!

Joe
www.joesackey.com

 

"I live my life 1/4 mile at a time. For those 10 seconds, I'm free"

~~~~
either that, or somebody drives a Mac Truck

 

Pro: arguably less wear to synchros

Con: definitely more wear to clutch and throwout bearings


Which is 'better'??? I doubt there are any long-term studies. And synchros are not particularly less expensive to replace than clutches and throwout bearings anyway.

Personally, I generally do not double-clutch, unless I am in the mood for a silky smooth drive without perfect engine-RPM matching. It is, however, of particular use to English prats who prefer the kind of "driving" involving driving gloves, sub-speed-limit velocities, tea and bragging of their car's performance (which they have never come close to experiencing), so I think our resident git would be well advised to double clutch to his heart's content and be sure to tell us all about it as verbosely as possible.

 

a) - Mack trucks now have autoboxes, and fat ladies drive them.

b) - only 10 seconds? Don't hold back, go ahead and step on it. Those clutch packs are cheap enough.

 

Come on, you surely know what I'm referencing.... the worlds "greatest" performance driving movie of all time

"Your Granny Shifting, and not double clutching it like you should"
"I almost had you"
"Had me? You never had nothing, you never had your car"

or something similar

 

You mean you use a clutch when you shift? Geez, real mean don't use clutches.... A "clutch is a crutch" is the conventional wisdom.

That said, when I learned to race cars, the first thing the Skip Barber and Russell schools taught was the double de-clutch, then shifting up without the clutch and then shifting down without the clutch.

I do belive you answered your own question futher down the thread.

Steve

 

From my extensive reading on the subject....in summary. Double-clutching ONLY serves an advantage on a non-synchromesh gearbox. Pointless on a car with synchros.

 

nthfintiy, I do not really know what ANYBODY on this thread is actually referencing, just to tell you the truth.

My knowledge of such matters began when my old 67 Corvair parted it's clutch cable - and I proudly refused to accept a tow. I showed off my abilities to my mechanic, saying - I have learned how to shift without a clutch.

He replied - you are NOT shifting without a clutch, you are just using your synchronizers for a clutch...

 

Double clutching to downshift is pointless when not paired with it's hot sister, rev matching.

 

I almost always double clutch/rev match/heel and toe in everything from my 73 Porsche 911 to 96 Jeep Cherokee. I have noted (on down shifting) that it seems to always provied a smother shift as felt through the shifter and power band. Both of said vehicles probably have weak synchros as especially when cold "granny shifting" results in much gear grinding and/or very very stiff gear changes. Double clutch/rev match alleviates this problem entirely (when done correctly).

As our doctoral student pointed out the purpose of this excercise is to match your transmission output shaft and input shaft (as a ration of the gearing, aka layshaft/mainshaft) in speed, ergo bypassing the "synchros". I find it especially useful when say, downshifting going into a turn to get the right gear with the least effort, and have the engine at the ideal RPM to begin accelerating out of the turn.

If you are doing "clutchless" shifting, then you also have to revmatch to get the gears to agree with one another. I enjoy practicing that as well, and upon lack of a non-synchro transmission it seems the best way to practice rev-matching for said double clutch downshifts.

As for Mack trucks, I am a MACK employee. I assure you we still install manual transmissions, as well as automatics, however I believe the manuals we now use are fully sychro'd. However in some/most/all states the license test for a CDL must still be done with a non-synchro manual.

 

And their barely-legal cousin, heel&toe...

 

What happens if you're going 120mph and you're in a high gear and need to stop in a heartbeat? Do you have to go back down through 5,4,3,2,1? I wouldnt worry.

 

It will not only wear the clutch faster, but if you blip the throttle when you do it the extra fuel will wash the oil off the piston rings and result in more wear...especially in carb cars...

 

Actually, if the fly wheel is light enough, it will offer advantages in terms of decreased shift times. A fast revving race engine can change its RPM faster than the synchro's can make up the difference. In my Porsche, I onlydouble clutch if I have a large RPM difference when I'm not in a hurry, as the motor's fly wheel is big enough, I could punch it harshly into gear faster than the engine can change speed. I also double clutch when cold, as the gearbox is in the back, and won't warm up much with engine heat at all.

 

When slowing down hard and down shifting in a race car with a tight locking rear end, you have to rev match by revving it up as if you were double clutching, otherwise when you release the clutch you lock your rear wheels. Although I don't need to do this with the 550, either because it doesn't lock tight enough, or because I don't drive it hard enough, I do it all the time just to hear the V12 howl.

Ferrari, it's all about pleasure...

 

So funny this was brought up, in that terrible film, they were drag racers...why would you double clutch when going UP a gear, which is all they do? ugh.

 

1+

Someone has been watching to much fast and the furious to believe that crap works.