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Im young and Im new to driving stick, so Im sure this is a very silly question to most of you but I have to ask it anyway. While driving the car one day I tried pressing on the gas pretty hard while I was changing gears and when I shifted I noticed I got a little bit of a boost... I guess because I was keeping the revs up. But anyway my question is this: Is that bad for the car or no? And isnt there already a name for this technique?

LiveToRev

Did you feel a jolt from the drivetrain? Did you clutch in, release the throttle, shift, clutch out, then depress the gas petal?

Ike

It's called not driving like a pansy

tuj

If you are saying that you rev'ed the car with the clutch in, then yes, basically that is not so good for the clutch during upshifts. There's no real reason to do it, given that on an upshift, the flywheel will carry all the inertia you'll need for the next gear. Unless you have a very extremely lightened flywheel and are racing, you should always be entirely off the throttle when the clutch is moving on upshifts.

Downshifts are a different deal, and rev-matching is essential for avoiding shock to the drive-line. Its also easier on the clutch. That being said, the RX-8 transmission responds much better to double-clutching. You can aim a bit high on the revs and still remain smooth, whereas with single-clutch downshifting, you need to be pretty precise with the rev's and any overshoot will result in drag and disruption of the drive-line.

zoom mobile

I did press the gas while stepping on the clutch, but i was only on the clutch for a tenth of a second or so.. basicaly i was pushing the car when i was doing this and trying to shift as fast as possible, so my foot was only on the clutch for a fraction of a second.

RenesisRacer

I think what you are reffering to is called speed shifting or powershifting. I'm not too knowledgeable about drag racing but I think they use it to get that little boost each time they shift. If you do it too much it can creat a lot of heat in the clutch which could burn it, and that's no fun, plus it's sending a jolt through the gearbox and the entire powertrain. Not to mention your passengers could toss thier cookies, which also would'nt be fun.

Jdunsh

I've read a few things on the internet about double-clutching but still don't understand it too well, could you explain it caveman style?

RenesisRacer

double clutching is basically shifting into neutral before shifting down (or up) a gear.

Driving in 4th gear
Clutch in
Shift into neutral
Clutch out
rev the engine to match the engine's speed to the new gear
clutch in
Shift into 3rd gear
clutch out
drive on

If you're shifting up you wouldn't rev the engine, just let them fall to match the higher gear.
You don't really have to do it unless you're turning the block without stopping and need the torque, but it's fun, smoother, and it sounds cool.

Sigma

Basically, as you may have already noticed, as you downshift you have to allow the clutch to slowly (relatively speaking) slip into the lower gear. Otherwise, if you were going from 5th to 3rd and let off the clutch in a hurry, the entire car would jerk harshly and put tremendous strain on the clutch and pressure plate, because you're going from 5,000 RPMs in 5th, the engine starts slowing because you lift the throttle to shift, and then instantanesouly when you let off the clutch it goes to to 8,000RPMs in 3rd -- Bad idea.

The solution to that is "double-clutching" -- getting both the transmission and the engine spinning at the same speed, so when you let out the clutch you can do it very quickly and very smoothly. You do this by "blipping" the throttle. Just how much depends on what gear you're in and going to, and how fast you're going.

In the above example you'd press the clutch in, shift to neutral, let out the clutch, blip the throttle from the 5,000RPMs that you you at to 8,000RPMs that you will be at (actually you need to go a bit higher because it will immediately slow down and the process takes time), push the clutch in again, shift to 3rd, then let out the clutch for the final time.

If you did it right, you can do it incredibly fast and put virtually no load on the clutch or pressure plate as everything is spinning at the same speed when it all mates together.

Mikelikes2drive

i thought double clutch wasnt needed with todays synchros, but nowadays you only need to use single clutch? i remember hearing this in a performance driving vid.

Ike

That's prettymuch true and what Sigma just described is rev matching not double clutching.

Double clutching is usually during an upshift and entails pushing the clutch in after taking your foot off the gas. While the clutch is depressed you shift the car into neutral and release the clutch. Then usually wait a tick or two for the revs of the engine to come down, depress the clutch again, upshift and release the clutch while applying the proper amount of throttle. Unless you drive an 18 wheeler double clutching is prettymuch useless nowadays. The only time it really has any use on most modern cars is when first gear is tricky to downshift into double clutching can sometimes help, though the biggest help is that you've slowed down a bit in the process most likely.

tuj

Double-clutching was mandatory on old-school cars without syncros for downshifts. On an upshift, it doesn't matter nearly as much, and often even using the clutch at all on crash boxes during upshifts is unnecessary.

The whole point of this is that you want the car to remain smooth when you downshift. There are 4 ways you can downshift to do this:

-clutch in, shift down, slowly let clutch out. This is the clutch drag method that most people do when they first learn to drive a stick. Its easy, but its not so good for the clutch, plus it doesn't really work when you are driving hard.

-clutch in, blip the throttle to rev match, shift down, clutch out. This is the conventional rev-match technique that most people use on modern trans. with syncros. Its very quick, and therefore ideal to use with heel-toe'ing. The disadvantage is that you must be pretty close on the throttle blip to where the rev's will end up in the lower gear. If you undershoot, the clutch will drag, and if you overshoot, you'll get some lurch. On a non-syncro car, this technique will not work due to the fact that the layshaft and output of the transmission are at two different speeds, you won't be able to get into the lower gear.

-clutch in, shift into neutral, clutch out, blip throttle to rev match, clutch in, shift down, clutch out. In this case we have put all of the speed matching between the layshaft and the output of the transmission. Now why would you do this on a modern car? Well in this case, you can overshoot the revs a little bit and still stay very very smooth because the syncros basically take up that extra energy and smooth the whole process out. Its also a bit easier on the syncros because the speeds are closer together inside the transmission so they don't work as hard. Using the clutch each time decouples the engine from having any influence on the layshft during this procedure.

-no clutch, shift into neutral, blip throttle, no clutch, shove into lower gear. The no-clutch method can work if you are really good. Its probably the fastest of all of them and still remain smooth, but now you need to get the rev's exactly right because you can't rely on the clutch to smooth them out, nor can you rely on the syncros (if you have them) very much because the layshaft will be influenced by the engine.

For driving hard, single-clutch rev-matching in combination with heel-toe is usually ideal. I started learning double-clutching because I was at an auto-x that required me to go down to first gear and it was about impossible to make that shift with single-clutch rev matching. I've since found that if I double clutch, I can make that shift pretty easy. Its a nice technique, the only problem is the extra time it takes to do.

shocar

I developed the double-clutch habit when driving a manual with a very notchy transmission. Double clutching in used in down-shifting. It is a variation of heel-toe downshifting for which the throttle is blipped with the cluch pedal pushed in. On many transmissions there is still a significant force exerted on the the transmission shafts even with the clutch pushed in and that is why blipping the throttle with the clutch pedal pushed in is able to spin up the shafts for syncro speed matching for the down-shift. On more clunky transmissions, it is necessary to put the transmission in neutral and let up the clutch pedal before blipping the trottle. This spins up the shafts and then the clutch pedal is pushed in again while the shaft revs are droppping. Selecting the down shift gear as the revs drop is easier in this case. You just have to make sure that the shaft speeds are blipped higher than the natural engagement speed of the syncr for the lower gear. So I habitually do this now on all down-shifts.

Sigma

Double-Clutching and Rev-Matching are essentially the same thing, the only difference is that in rev-matching you don't shift the car into neutral and let off the clutch to blip the throttle, in double-clutching you do -- which is what I described.

RUmble

Great thread. I learned alot here.

916mph

For the most part that's true.

But if you're in an engine that makes its power up top, sometimes it's useful to downshift to, say, 1st gear, at 30mph... try doing this - it will be very hard - the synchro has a hard time matching up the tranny speed, so if you shift it to neutral, rev it up, and THEN shift into first, it'll be a lot easier, and will sound cooler too .

Ike

Umm, you're only pushing the clutch in once with rev matching, which is why it's rev matching not double clutching since there is no double of anything involved

acc3d

I thought it wasn't advisable to downshift into 1st unless you were going less than 10mph. I usually can't get it into 1st unless I'm going 7mph or less...of course I never tried double clutching.

I'd love to get it into 1st to power out of turns better.

Sigma

Which is exactly what I said -- "the only difference is that in rev-matching you don't shift the car into neutral and let off the clutch" (hence you're only pushing the clutch once). And, in my description of double-clutching I described exactly the same steps as you did, but you said I described rev-matching.

We're saying exactly the same thing, something's just gotten lost in the translation.

Rx8bydocabe

ok, the clutch is in, what's better blipping the gas before you down shift or after you down shift? and why?

Sigma

If you're just rev-matching, it doesn't matter if you're in Gear or in Neutral when you blip the gas. Blipping the throttle in neither Neutral nor in Gear with the clutch in won't get the layshaft spinning at a different speed, which is why there is double-clutching.

If you're going fast enough you might find that you have to double-clutch, and blip the throttle in Neutral with the Clutch out, or else the car won't allow you to get it into the lower gear at all.

Jdunsh

Thanks for all the input from everyone, very informative.

Ike

We're not saying exactly the same thing... The purpose of double clutching is partly so the revs of the engine come down before an upshift. Bliping the throttle defeats the whole purpose of why many people double clutch and doing so in a tranny without synchros (where double clutching is most often used) is a very bad thing.

Sigma

I think it goes without saying that you wouldn't blip the throttle on an upshift, and that you would instead allow the revs to lower. That'd be pretty stupid and pointless. But the question about double-clutching was posed in regards to downshifting so that is how I described the situation.

I was describing double-clutching on the downshift (since that's what the conversation was talking about), you described the process on the upshift. But the process described was exactly the same. You called what I described rev-matching when that was NOT the case, as rev-matching is something entirely different.

Now, if you could please tell me how the below steps are "rev-matching" (since that's what you said I was describing), I'd appreciate it. Because you're only further confusing people with your misinformation. Unless of course I'm the one that is incorrect, at which point if you can tell me why I'll gladly concede that I'm incorrect.

Ike

In your first post I somehow missed the "push the clutch in again" part and finally see it now that it's in quotes, really sorry about that

I don't know why were debating it anyhow, it's useless on todays cars for the most part and there's no good reason to double clutch other than a car not wanting to downshift into first on an autox course. Even then it's usually best to stay in second the whole run, but from time to time it will improve your times on an autox course depedning largely on course layout and the specific cars gearing.

acc3d, downshifting to 1st isn't a problem as long as it seems to shift smoothly. If it's tough to get into 1st gear then yes it's best for the longevity of your tranny to not force it or double clutch to try and get it into 1st.