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The other night my friend and I were talking about why is double clutching necessary, when rev matching seems like the exact same thing but easier? After some research and test driving, we got a solid answer and I wanted to share it with you guys in case anybody else had the same question

Rev Matching

What is it?

Rev matching, or revolution matching, is when you bring up the RPM's of your car to "match" the next gear you are downshifting to. There are many reasons and benefits to doing this; mainly, it will allow you to shift into gear without any hesitation or jolting. It also reduce the strain on your transmission if done correctly.

The reasoning behind rev matching is that the current gear the engine is on will not be spinning fast enough to seamlessly switch to a lower gear. By increasing the RPM's beforehand, you will allow the engine to switch to the lower faster moving gear easily. If done correctly you will feel no jolt or hesitation and can accelerate much more easily.

When do I use it?

Typically, rev matching is used for two occasions. The first application is when you need to downshift without slowing down for a quick acceleration. The second is when coasting, and you need to get back in gear to add speed again. Simply match the RPM's to whatever gear you need to be in, and re-engage said gear.

Of course, there are other uses to rev matching. These were just two situations that I thought of that are the most practical.

How do I do it?

It's simple once you get the hang of it. When driving, hold in the clutch, apply gas to raise RPM's to desired level, downshift to lower gear, release clutch, enjoy. The tricky part is getting the RPM's to the correct level, but it really is quite easy.


Double Clutching

What is it?

Double clutching has the same principles and reasoning as rev matching. However, it is different in few ways. Double clutching is used only for huge accelerations, and in this aspect should only be applied for racing.

A double clutch is when you want skip one or two gears to downshift quickly, and increase your engine RPM's drastically to allow a seamless shift between 5th and 3rd, for example.

When do I use it?

Let's say you're on the highway, and some asshole decides he wants to race you with his rice machine. You're cruising in 5th (or 6th for you speeds out there), and decide to double clutch back to 3rd so you can have a massive acceleration as you will be into the 6k powerband area.

How do I do it?

Double clutching is just a tiny bit more difficult than rev matching. When driving, you engage clutch, shift to neutral, release clutch, apply gas, engage clutch, shift into desired gear, release clutch. This is where the name "double clutch" is derived from, as you end up engaging the clutch pedal twice quickly.


Double Clutching vs. Rev Matching

After realizing the difference between the two methods, I wondered why it was necessary to shift to neutral for double clutching. Why is that extra step needed, when you can just hold down the clutch?

There are two reasons for this. First, when in neutral, the engine can accelerate at a more rapid pace. If this confuses you, think of it this way. When backing up in reverse and you hold the clutch in, you can still hear the gear winding up. This is because the gear is still set in place, but holding the clutch down makes the engine act as if it is in neutral because it is not connected. When you shift to neutral, no gear is engaged which allows it to increase RPM's at a much faster rate.

The second reason is to save the synchros and clutch from being worn out more rapidly. When rev matching, no damage is made from changing the RPM's up by 400-1,000 while holding the clutch in, assuming you're driving at regular speeds. But when double clutching, you are increasing RPM's by more than 2,500 rapidly, which can cause a strain on your clutch and transmission if you are still in gear.


Conclusion

There is the main difference between the two shifting styles. In short: use rev matching when downshifting only one gear, use double clutching if downshifting more than one gear. If anyone has anymore knowledge to add, feel free. Hope this cleared up the difference for those of you who didn't know.
 

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100% CANUCK
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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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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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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!
 

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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.
 

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Discussion Starter #7
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.
 

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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!!!!!:mad:

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




As for the shifting just
:drive:
 

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Someones been watching a little too much fast and furious lol
 

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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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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.
 

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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.
 

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


...to change your transmission fluid ;)
 

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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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.

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
 

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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.
 

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Yes, because your parents as adults should know better
I meant that as a joke. I'm a responsible person, and that's why my parents trusted that they could teach me it. My cars have only been driven "fast" twice, and neither time was I driving. I had trouble getting my downshifts smooth; that's why they taught me.
 
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