no wonder you are still in the 13sec club

 

no offense taken. you obviously know how the inside of a tranny words better than i do. and i appreciate the education.

double clutching is an old technique that was improperly used in fast and furious.
in all my times road racing, i've never ever double clutched or done a clutch double tap while downshifting

 

Yeah FnF had it all wrong...
You're right, though, with modern trannies it's not needed because of the synchros. However, when driving very hard in high rpm, the synchros see a great deal of wear. If you can rev match accurately, you can still carry a very smooth line and downshift like warm butter. Upshifting doesn't wear the synchros much, because the'yre helping the input shaft to naturally slow down. forcing it to speed up, is much harder and causes more wear..

In some racing transmissions or "dog boxes" that don't have synchros, the driver is able to shift hard into gear and the dog teeth just grab and go. Daily, this would be a huge headache because the car needs to be driven/shifted kind of aggressively.

Double clutching was required because there was no way to speed up the input shaft before synchros.

So, if you let the clutch out in neutral (during a rev match) the input shaft speeds up without using the sunchro at all (because it's not in gear). Push the clutch in, shift, let clutch out. It's smooth like warm butter and the synchro did nothing. Why? Because by the time you put it into gear, the two shafts were already speed-matched so it just slips into gear with almost no resistance.

 

Very patronizing of you

I have found that double clutching on the downshift takes only slightly longer than just rev matching. It also preservers the syncros and generally makes for a smoother shift. There are also times, such as dropping to first gear while moving at about 5 mph, that it is impossible to shift unless you double clutch.

Another thought about the additional time required. Usually when I am down shifting I am also under braking. It is usually anticipated as well as not time critical. I am doing it to prepare for the next corner and the additional time makes no difference.

I have found that most people that make blanket statements about the uselessness of double clutching generally can't do it. They justify their technique by claiming people who do double clutch as "you dont' know what you are doing" instead of bothering to learn themselves.

 

here's a great read on the inner workings:
(btw this website is a wealth of information)
http://auto.howstuffworks.com/transmission.htm

 

good find wheel, thanks for the education.

JTB, i didn't realize i was patronizing till you posted. I didn't mean to come off as an ***. When I said you, i didn't mean the poster or you personally, i meant it as in general population.
I know double clutching and heel toe, i just dont' know the inner workings of a tranny as you see Wheel ecucated me on.
I just don't like people posting thinkign they know something when they actually know nothing and present misleading or false information.

 

there is no reason for double clutching a sycronized transmission. match reving using heel-toe works just fine. commercial big rigs with non-syncronized trannys are the only things you should ever have to double clutch... but i hardly ever do that.... i don't use the clutch after 1st gear. you just got to make sure your revs are right when you try to go into that next gear.

 

No problem on the patronizing -- people often misread my tone as well

I also understood the "you" as not targeted at me but as a general term such as "one". I just didn't agree that double clutching is useless or that those that use it don't know what they are doing.

"I just don't like people posting thinking they know something when they actually know nothing and present misleading or false information." -- I agree completely

 

This point has been mentioned several times. You're right, double clutching IS needed for non-synchro transmissions. In modern synchro'd trannys it's not NEEDED, but is VERY USEFUL as it can dramatically reduce synchro wear upon downshifting, when the most wear happens.

For daily driving, double clutching isn't necessary, but at high-rpms the synchro wear is much greater, so DC'ing helps to extend the tranny life.

 

JTB, I think he (ldstang50) posted after my post commenting on a post by slow_evo who said that there is a double clutch up-shift technique for drag racing. Something which I see as more of a waste of time cos you're effectively coasting in the middle of a drag race.

I agree that rev matching, double clutching, heel-toeing is generally a 'good thing' for lap times and wear. However, it is no instant fix and the effects vary between tracks. I've seen many people try it and actually go slower - it's an awful lot to do and think about. Obviously if done properly with proper practice you will at the very least get the same lap time with considerably less wear on your tranny, but I think a lot of people get the idea that if you double clutch/heel-toe etc. you will instantly be quicker and find out that it's not so and therefore conclude that it's a useless technique.

 

Possibly. However this piece of his post seemed to be referring to slowing down -- note the reference to heel toe.

I agree that double clutching will not make you faster unless you are missing shifts. Heel toe, however, definitely will as being smooth as well as maintaining an appropriate gear is always quicker.

 

After reading all of these posts, I am even more confused as to the definition of double clutching than I was before reading it. Could someone who actually knows what they are talking about please give a side-by-side comparison between double clutching and rev matching, that way I know why they are apparently two completely different techniques for two different purposes... or are they?

 

Thanks for presenting a real question with a definite answer and not just a bunch of misrepresented opinions lead by a misunderstanding of the techniques being discussed. I may overlap a lot of previously discussed material, but I'd like to put enough prerequisite information in here to help out urbanknight.

Rev matching is a technique used to match the speed of the input shaft to the speed of the output shaft of the transmission in short, and is a technique that is supplemental to and required in order to successfully double-clutch. Rev-matching can and should be done during any type of downshift, but is especially important and helpful at higher engine speed, whether it be single-clutching or double-clutching (single clutching is what you most likely do if you don't know what all these terms mean). Use wheelhaus' suggested link of howstuffoworks... it's an awesome resource and it puts all the concepts into easy-to-digest sections using very simple and readable terminology. I learned a large amount of basic concepts there and went on to research topics further, having a confident understanding of the basics.

The term heel-and-toe downshifting refers to the technique of rev-matching while applying pressure to the brake pedal simoultaneously with the right foot, so as you can properly rev-match, shift, and brake at the same time. In this case as well, rev-matching is a general supplemental technique that is the main idea behind specific techniques and applications of downshifting.

Some people may also comfuse the differences and similarities of double-clutching and heel-toeing. Yes, you can do both at the same time and yes, this is beneficial in many cases. A lot of the time this is only considered worth-while if you're revving fairly high and keeping the weight distribution constant is important. On the track with a steet manual gearbox, heel-toe double-clutching is a very good idea, especially on a complexion of corners that you must connect into one turn, and especially when you want your gearbox to last you a long time. Wheelhaus is correct in the quote below:

In its most simple form, rev-matching can be used during single-clutch downshifts, and some may improperly call this application of the general technique "rev-matching" when rev-matching is only a part of the process and this technique is properly called "single-clutch downshifting."

As far as real world application... if you don't drive spiritedly ever, it's fine to stick to single-clutching if you're not interested in trying to teach yourself other ways to downshift. If you do any type of spirited driving, road racing, auto-x, rally-x, etc. it is a very good idea to practice these techniques at all times, even while driving on the streets. Once again, heel-toe rev-matching is a prerequisite to double-clutching. There are TONS of resources regarding how to teach yourself heel-toe and I find that the RalliArt pedal set-up allows for a somewhat naturally-feeling heel-toe( though it is easier to make precise alterations of accelerator pressure while brake pressure is substantial). Once you can comfortably heel-toe on the streets, try your hand at double-clutching with your feet in their natural driving position and once you're confortable doing that, try your hand at combining the two. It will come with time. I naturally double-clutch every single downshift (with the exception of the occasional 5-4 single-clutch) and I heel-toe & heel-toe double-clutch between a quarter and a half of my downshifts, depending on the situation (and I'm only 16 years old!).

JTB has a very good point here... all of the downshift techniques being discussed have a purpose, and when used properly can make improve track times, decrease tranny wear, keep F/R weight distribution constant and therefore predictable while cornering, promote understanding of the modern manual transmission, help the driver stay actively involved in driving, etc. If you think double-clutch downshifting is pointless, you either tried and gave up too easily, or do not fully grasp the concept (which can lead to the tring and giving up).

Please read the above paragraph about the reasons for double-clutching. It's obviously not required or essential during everyday driving, but to say that there is no reason for it is an ignorant statement (no offense). When you say you don't use the clutch after first gear, does this mean you drive a WRC car or you wait for the sweet spot of each gear and slam it into the next one without depressing the clutch? This statement comfused me.

If I got something wrong, please let me know kindly. I said a lot so I probably got one or two details wrong. If, however, you disagree with my opinion, please explain yourself thoroughly.

[/typing forever]

 

I'm as curious as blackhawkRA now. It's possible to go between gears without the clutch particularly up-shifts and it is possible to do down shifting but I would guess that doing to the whole time would eat your snychros and your shifts will be fairly slow (comparatively long period between gears). You'll have to be pretty darn good at 'getting the revs right' to avoid munching the synchros and while doing that while racing is one thing, doing it on the streets is something else completely.

I've certainly never heard of anyone who does this on a regular basis - perhaps I'm misled...

 

its possible but hard to do and bad for the transmission