Nice little conparison there. I dont use either technique and likely never will. IMO neither is needed for driving a car.

I believe that both techniques are more used by truckers, and even then, not all that often. Most truckers dont even use the clutch except for 1st & reverse. Rev matching is used lots for downshifting by truckers as there are no synchros.

Synchros eliminate the need for rev matching as they are making up the difference in speed between the two shafts in the transmission which are spinning at different speeds.

Double clutching just seems like a waste to me. Just seems like you are wearing everything out twice as fast due to unnecessary use.

Thats just my 2¢ Im sure tons of people use one or both techniques but i just dont see a need for either of them driving a car.


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^ THIS!!!


I messed around with both of these in my old crappy 93 corolla. Damn fun drifting that thing and heel-toe was definitely needed, but yeah, these aren't needed with our cars. Go right ahead and do it anyways if you want, just be aware that they both put significantly more wear on your clutch/trans than shifting properly.

Good comparison either way though.

 

I feel like its more for racing and the occasional downshift you may need in heavy traffic... this thread now has 4 cents

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I feel like its more for racing

Is it weird, then, that my parents taught me both of them?

 

There is a great explanation of this in the Skip Barber book on racing. If you're technical, it makes for a great read. Here is a few points of clarification for application on the track:

These are not exclusive - it's not "either - or". And both are used for downshifting. In fact, most race drivers use the double clutch downshift to allow rev matching. It's that throttle "blip" between the clutch applications that allows the engine, or more correctly - the input shaft speed - to match the revolutions necessary for the vehicle speed and chosen gear.

The double clutch allows two shifts - from the higher gear to neutral and from neutral to the lower gear. A professional driver will not skip gears. Even if they do not use it, they will pass through a gear on the way down. That stop - milliseconds - at neutral allows time for the blip to the engine to bring up the input shaft RPM. Yes, that saves the syncros and transmission in general. The thing to remember is that even though the clutch disengages the transmission, the input shaft does not completely stop, even in neutral with the clutch in. It will still be spinning. So that stop at neutral takes advantage of that to complete the rev match of the input shaft to the transmission.

As far as acceleration/upshifting - typically in rapid acceleration, the engine speed does not drop far enough for any additional "rev matching" to be necessary. It does it by the nature of the quick up-shift. Usually by the time you clutch, lift, shift, and press, the engine has dropped just enough to match the revs on the upshift. And it is an order of magnitude harder on the transmission to not use the clutch. Clutches are much much cheaper than transmissions!

 

You do not need double clutching if you have a synchronised transmission. Which we all have.

tapatalking.. err wait.

 

Thanks for all the cents haha input is always nice to have.

Personally, I feel that a correct rev match is healthier for a transmission (as it allows shifting with much less effort) and can extend the life of your transmission. When I rev match it feels super smooth with no bumps or anything, and I don't feel the car pulling or fighting the downshift if I need a quick acceleration for an on ramp or passing.

As for double clutching, I don't really think ill use it at all but it's good knowledge to have I suppose. In the end it's all about how you drive I guess. I'm still learning how to heel-toe properly, that technique is harder than cold nipples on a winter morning.

 

Double clutching is good if you drive a big rig lulz. I rev match on downshifts but only because I have seriously aggressive clutch.

 

yeah ya do you lucky bastard!!!!!

Can you get that thing to chirp into forth yet????




As for the shifting just
:drive:

 

Someones been watching a little too much fast and furious lol

 

Sometimes I wish this was msf lol.

Just kidding, but really...like everyone has basically said, no need to double clutch on our cars or really any modern car for that matter that isn't 15 or 20 years old. It's really a trucker thing more than a race car thing anyway.

Regular rev matching on the other hand is normal and obviously helps with downshifting as you can feel the car transition smoothly and not rock like you have a broken engine mount.

This comes up every once in a while on the forums usually from some hardcore F&F addict who is dead set on believing that double clutching is saving his tranny and gears or helping whatever the movies tell him lol. But you posted some actual interesting info, was a good little read for me here restless at 4am hahaha.


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.

Regular rev matching on the other hand is normal and obviously helps with downshifting as you can feel the car transition smoothly and not rock like you have a broken engine mount.

Or you can slowly let off the clutch and it won't rock......

Is it weird, then, that my parents taught me both of them?

Yes, because your parents as adults should know better

I mean OP, I don't mean any disrespect to you at all. But seriously, put away the Fast and Furious DVD's

What you said

Thanks for all the cents haha input is always nice to have.

Personally, I feel that a correct rev match is healthier for a transmission (as it allows shifting with much less effort) and can extend the life of your transmission.

NOW this is just me thinking out loud, but....This " saving your transmission" thing. Where did you get this "feeling"? Nothing about shifting will hurt your transmission if done properly. I.e not power shifting, going WOT and shifting. No daily use of NOT rev matching has been or will ever be proven to be bad for your transmission

 

I may have missed this somewhere in the thread, but the real reason for double clutching and the reason that you put the transmission into neutral with clutch engaged (out) is to spin the input shaft up to speed. Simplified, to engage gears (upshift or downshift), the input shaft and output shaft in the transmision have to be spinning at the same speed so that the dog teeth can engage without awful grinding. On upshifts, you need the input shaft to slow down to match the higher gearing of the output shaft and friction and inertia automatically does this for you. On downshifts, the input shaft needs to be sped up. Just blipping the engine with the clutch in (disengaged) won't accomplish this since the clutch disconnects the engine from the transmission. The engine might speed up, but the input shaft doesn't. So you have to put the transmission in neutral first, then let out the clutch, then blip the engine to speed up the input shaft to match the lower gearing of the output shaft.

The synchros are designed to take care of this for you so you don't have to worry about it. In the old days, synchros would wear out and double clutching would both extend their lives and allow you to shift when they were worn on a high mileage car. So it used to be important to know how to do. Nowadays however, synchros are robust enough that they will outlast the car unless you're a really abusive shifter.

Rev matching is still a good idea as it makes for smoother driving and less drivetrain shock.

 

Is a serious thread? I'm not trying to be a dick or anything, but seriously?

I've driven the shit out of cars ( I've had about 25 cars, 90% of them being manual), this whole " strain on the transmission" from normal shifting. No, just no. Cars are built for shifting. No manufacturer tells you when you buy the car. " Hey guy make sure you rev match so you don't hurt the transmission"


And this double clutching shit? LOL give me a break. I've been to the track a few hundred times, street raced probably a few hundred times. I've NEVER had to do this double clutch crap. If I'm in 5th, and someone wants to race, I just push the clutch in, and slam 3rd and haul ass.

 

EXACTLY!!

F&F made everyone think you still need to double clutch. These two techniques are only used by truckers. Most truckers only rev match. They rev match on all shifting & dont even use the clutch. Clutch is only used for getting going from a stop.

In Ontario, truckers are usually expected to double clutch on their road test for their licence.

Reason for this is that there are no synchros in their transmissions. F&F is responsible. People need to stop over thinking & just get in and :drive:


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The best thing you can do for your transmission is...


...to change your transmission fluid

 

Alright, where do I begin...

lol for the F&F inquiries, no I did not start thinking about this from the movies haha so basically every Sunday I go to my friends house for Mod Day Sunday (it's a little thing we started, we just use it as a day to work on our cars). So we went to Ace Hardware to pick up some sandpaper and masking tape, and we started talking about rev matching. I had known about it before, and I use it occasionally, especially when I'm coasting on the highway and get back in gear. It's way better than jolting into gear with no revs, just saying lol.

Then the topic of double clutching came up; I hadn't really heard of what it was too much, just that it was mentioned. We learned up on the topic, and thought it was the same thing as rev matching. Then we tried it out later, skipping gears in his scion and whatnot hahaha it was a blast. But it doesn't really make that much of a difference. I mean, yea it speeds up faster and you end up taking off QUICK but the real world application of it was nigh useless. So after our little escapades were finished, I decided to post up a thread on it in case anyone ended up with the same questions as we did (why double clutch?).

Now, as for rev matching being useless, I wouldn't say it's completely obsolete. For regular downshifting, I feel no need for rev matching. I didn't say anything about that in the OP. It is completely useless in that sense.

As for the acceleration purpose, it is indeed useful. When we were testing it out downshifting from 4th to 3rd without slowing down and to get that speed boost, no rev matching created a huge jolt that you could feel through out the car just using the clutch. This was at 4th at approx 2.5rpms. That was to be expected of course. We got the speed boost, but the jolt felt uncomfortable to say the least and lost us those few seconds when the car could've just been accelerating. After attempting the same situation, this time with rev matching, there was no jolt and the car jumped gears easily. No jolt, instant acceleration. The evidence right there was all we needed.

I appreciate all criticism and input, don't worry you guys aren't hurting my feelings lol. Hopefully that explanation cleared up some stuff, if not oh well.

 

Smooth downshifts are boring

 

Put an agressive clutch in and let me know how smooth those downshifts are haha.

 

Haha maybe when my clutch blows lol what stage is yours?

 

Exedy 2+

 

You sonofabitch.

 

Nice one man, how small is the engagement window on that? I'm assuming you got a lightened flywheel too huh

 

Yeah I have an exedy lightweight prototype. I actually got it all for free lol. The clutch does not slip well for daily driving. Its engagement is pretty tight.

tapatalking.. err wait.

 

What!! Where you a test fit or something? That's really cool, but is that clutch more trouble than it's worth?

When mine blows I want to get a stage 1 clutch masters and exedy 18 pound flywheel lol

 

Yeah I was a test fit. They paid the labor and flew out to over see the install. Was a really cool experience. I love the clutch. My wife however hates it but she hasn't really driven it much.

tapatalking.. err wait.

 

Wow that's awesome man glad you got to get that experience! Too bad they don't have any new products for our cars that need test fits now lol

 

I still don't quite understand double clutching, but I do know a lot about rev matching and it does extend the life of your clutch. Think about it, your matching the speed of the clutch so when the teeth engage there is no possible slippage before the clutch full engages. There is most commonly used on motorcycles.
Rev matching is useful. My only question is why can't you just rev match from 5th to 3rd? In double clutcing why l do you have to press the clutch in twice for any logic? What's the point of letting the clutch out in neutral and revving it then putting it in gear? Why not just pull the clutch in, shift into gear, rev, and then release the clutch?

 

By revving the engine when the transaxle is in neutral you are accelerating all the internals so they are spinning a bit faster than they will be when you enter the next lower gear. By the time you get the clutch depressed again and shift from neutral into the next lower gear the rotational speed of the transaxle has slowed to exactly the same speed (if you're practiced) that the engine will be rotating, and wheels turning, for the gear that you are entering.
Heel and Toe like Senna

 

And, when you get bored with all that you can do it all while braking hard into a corner.
Using your toe to brake slide your foot over to the accelerator pedal and give it a few quick stabs as you double-clutch your way down through the gearbox in a heel-toe fashion this will let you be in the perfect gear when you exit the corner and you did not lock the rear wheels (most ere rear drive when this came about) while they were unweighted while braking and entering the corner. You can enter the gear with the transmission going a little slower than the engine/road speed and drag the rear wheels into a bit of over steer. Doing this in a FWD will give you under steer (not much fun at all).
When my clutch went out in my 1-ton Landcruiser I drove for over an hour in stop and go traffic with only rev-matching shifting. Most of the shifts went okay... most of them.

 

I find the notion of ‘rev matching’ a bit peculiar if you don’t double-clutch the shift, too. Perhaps I grew up with too many non-synchronized transmissions, or trannies with weak or worn out synchros.

 

I ONLY double-clutch when downshifting (and of course rev-match) so, when I get a new or newish vehicle I DON'T ever end up with weak synchro's. Yeah, lotsa weak synchro used cars I've had in my life...

 

If you are rev matching perfectly without double clutching, i dont think youd run into any issues.

If the second or third gear synchro is worn on a fairly low mile , it's often a dead giveaway that the owner shifts at high rpm into that gear aggressively and often.

 

The correct sequence is a half-push IN of the clutch to take it out of the higher gear (and into neutral), then release the clutch pedal, rev to the correct rpm for the lower gear while in neutral (HOLDING that rpm 'till all is done), quickly push the clutch pedal fully down, immediately/quickly folowed by a decisive downshift from neutral to the desired gear (while holding rpm constant), and lastly release clutch pedal at normal pace (again, with engine revs still applied). Shift should occur smooth-as-butter, and your passengers should not even feel the shift.

 

Yep.

And it is entirely possible to up-shift without the clutch -- in fact, on a motorcycle it's utterly common to do so as each "throw" from gear-to-gear is identical in distance and form due to how the ratchet mechanism works in the gearbox although this is NOT recommended in a car. Why does it work? Because as you release the throttle from the lower gear the RPM falls and as it does the input and output match the next gear's requirement. Done right it slips right in. Done wrong, well..... Downward is much harder without the clutch.

Incidentally there should be little or no actual synchro wear with the proper gear oil and reasonable technique. The film formed by GL-4 oils is of lower strength than the synchro material (a brass compound) and shears first; thus, no actual metal-to-metal contact occurs. If you shift quickly and/or with a large mismatch between required and actual speeds of the input and output, however, then contact and wear does occur. I've got an MTX in my garage coming up on 300k miles and the #2 synchro, which is the one that usually wears out first, is perfectly fine (as are the rest.) I've not had a reason to take it apart but it's showing utterly no sign of distress. Then again I didn't drive it like Speed Racer and my daughter, who owns it now, doesn't either.

 

All the gears in a manual transmission except for reverse is helical cut, correct? A mechanic told me that if you're parking a manual car without using the e brake, to leave it in reverse to prevent rolling. As far as I know, reverse is the only gear which does not require a synchro.

Would it be feasible in a street car to have non helical cut gears for extra strength?

And, well, whenever your clutch does go on a street car, you're not completely screwed, so long as you can get the timing of each shift correct as the RPM's fall..

I know that in a last resort scenario you can put the gear into first gear while it's off and then when you start the car itll go into gear (albeit very violently) but in the case of a dead starter, how can you safely get a manual car started while rolling down a hill?