Rev Matching & Double Clutching
 

I have a general idea of what rev-matching is. However, I am curious about the RX8's specific rev-match tachometer gaps. How many RPMs is it per shift?

I also have no idea what double clutching is. Can someone tell me?

rev matching is all in the feel, there really isn't an RPM amount that you hit everytime, just tap the gas before you release the clutch and practice.

As for double clutching I believe its an old style shifting from the older trans of the 60's and 70's. To shift gears you would first press the clutch in, then shift out of gear, release clutch, then press clutch again and place into next gear, in essence pressing the clutch in twice or "double" clutching.

rev match/double clutching, while downshifting in brake zones is still taught at race/driving schools. with today's synchromesh gearboxes, it's a little redundant, yet learning the method provides sound driving technique for shedding speed and setting a car up to turn-in- the theory being that if the driveline is constantly engaged, it acts as yet another structural spine to steady the car's dynamics upon braking and turning... the method was more important before to conserve dogbox transmission gear life- again, not important in a street car with synchros.
many instructors which i've driven with don't practice double clutching in brake zones- and they're instructing at HPDE's (for whatever that's worth), so the method isn't essential to know, yet it is good practice to learn it.

example of double clutch / rev match braking....


4th gear engaged (for example)
approach brake point
apply brake force
clutch in
shift to neutral
clutch out
roll foot and blip throttle
clutch in
shift to 3rd
clutch out...
.....perform all of the above while maintaining consistant/linear brake force with your right foot on the brake pedal. continue down the gear selection, as needed, using the above method. it sounds extremely confusing, yet it becomes second nature after lots of practice. eventually, you can rev match extremely smoothly while braking as you learn (by ear and mph) the correct amount to blip the throttle and when.

I'm going to practice rev-matching (that roll foot thing) tomorrow morning, but I'm going to do it with the engine off. Will there be any damages to the car by doing it with the engine off? I did it once before, and I could practically hear the transmission shifting like they do in video games.

Anyone like to address the potention compression lock issue if you downshift without heel-and-toe and rev matching?

Not sure about what you're referring to. Only issue I'm aware of is that of locking up the rear end if you're not rev matching and you engage a lower gear with too much loaded engine speed.

Based on your response, I suggest further research on the subject before attempting anything. ;)
Good luck!

Compression lock... = "locking up the rear end if you're not rev matching and you engage a lower gear with too much loaded engine speed."

Time and time again I see people say not to drive like a pro :rolleyes: Old school rocks...

BTW anyone try to upshift without engaging clutch? You can you know :Eyecrazy:

Double clutching is a complete waste of time in a car with working synchros. The synchros will be faster than you every time.

+1 and I'm still waiting for the rice movie reference. I almost always heel toe downshift on the street and autocross though, it's pretty easy to do it in the Miata and S2000, the RX-8 pedal placement is a little uncomfortable for me though.

Yeah, I think Baghead has tried that a couple of times... :lol2:

Double clutching and rev-matching/heel-toe downshifts are really two different things.

Double clutching - as described above, the sequence goes something like this:

1. Enter the braking zone and apply the brakes.
2. Clutch in, shift to neutral.
3. Clutch out, roll foot and blip throttle.
4. Clutch in, downshift to appropriate gear.
5. Clutch out, engage lower gear.

Double clutching was a technique used with non-synchromesh transmissions in order to match speeds between the input and output shafts of the transmission. This is why you shift to neutral, let the clutch out (engaging the input shaft) and rev the engine (bringing up the speed of the input shaft), then engage the next lowest gear. In a non-synchro transmission or "dog box", if you don't properly match the speeds of the transmission's input and output shaft, the gears won't engage. This technique is redundant on a modern synchromesh transmission, as the synchros perform the function of indexing the input and output shafts.

Rev-matching/heel-toe downshifting - a different technique, which goes like this:

1. Enter the braking zone and apply the brakes.
2. Clutch in, shift to lower gear.
3. Simultaneously roll foot and blip throttle.
4. Clutch out, engage lower gear.

This is a technique used to bring the engine speed up to match the speed of the transmission input shaft. This technique is used in modern synchromesh transmissions to smooth the engagement of a lower gear under threshold braking, so that gear engagement does not upset the balance of the car.

Double-clutching is a neat skill if you can do it, but it really is redundant on modern cars. Rev-matching, however, is essential to driving a modern car smoothly at the limit under braking.

Unfortunately, doing it well takes a lot of practice. However, this is one of the few racing skills that you can legitimately practice every time you drive a car, without being a menace to society. If you practice it often enough it will become second nature, just like driving with both hands on the wheel. :)

"granny shifting, not double clutching like you should. Now me and the mad wizard are going to have to go through the engine and replace the piston rings you fried"

In a balls to the wall sprint race, it may be a waste of time.

It's not a waste of time when doing it as a sequence of motions sets up the car properly for turn-in and it establishes a rhythm for the driver to work with. In an endurance event, it conserves the drivetrain.

What I meant was that I heard a loud "GU DUK" every time I shifted with the engine off, like that ridiculous sound you get from shifting up and down in Need For Speed games. I'm not sure if that kind of noise is good for the parts.

In any case, I've googled it up, and no one talks about it. So I still have no idea if I should practice the motions with the car engine off.

You'll have to explain this sentence further, because it makes no sense to me. How does double-clutching "set up the car properly for turn-in" anymore than letting the synchros do the job for you?

It doesn't. The only thing it will do is save a little bit of wear on your synchros, if you do it right.

That said, I've yet to have to replace the synchros on any of the track/autox cars I've owned, even after five seasons and 120k miles in one case. I'll stick with heel-toe downshifts and leave double-clutching to the masochists. :rolleyes:

I was thinking of doing an arrive and drive race series in a formula Mazda. In order to do so, I'd have to complete a racing school.

I've heard that these race cars have gear boxes that require double clutching for heel/toe downshifts. Does anyone have experience with Formula Mazdas?

He is talking about heel-toe. Go driving around and go from 4th to 3rd gear and just dump the clutch. see how that feels. then try it again with the heel-toe methoid.

When you're lapping on a roadcourse, you fall into a rhythm of things, don't you?
So, let's examine a threshold brake zone at the end of a long straight going into a left hand turn.

You're entering the brake zone, in 4th gear, doing, say 100mph.
The turn is a 2nd gear turn.

One can:

a) brake, shed a bunch of speed, go into 2nd gear(4-2) , turn in .

or

b) brake while double (or single clutch if you may) down through the gears (4-3-2), turn in.

Either method is fine, yet the latter establishes a series of events, beginning from brake point to turn-in point which establishes a rhythmic procedure which helps one time the brake zone (which is good from a driver's perspective).

Going 4-3-2 while single or double clutching properly has the car settled in a smooth state, with no herky jerkyness about it when the gear is engaged. You hear blip, blip (as the gear selection goes from 4-3-2), yet you don't see the car lunge or surge, and the drivetrain is in harmony. That engaged drivetrain acts as another structural spine to the car, linking front to rear, keeping the dynamic of the car steady at turn-in (which is good from a mechanical/dynamic perspective).


Double clutching was taught to me by Jim Pace, class winner of 12Hrs Sebring and 24Hrs of Daytona. He double clutches in racing scenario to establish his rhythm and to conserve the drivetrain. If it's redundant and useless, I don't think he'd waste his time doing it and teaching it at Skip Barber race school....

...which leads to another topic, which is that Skip Barber is adamant about teaching double clutch rev match downshifting in brake zones. Every Skip grad - (both recreational and competitive) I've driven with, rev matches (and either single or double clutches) his gears though the brake zone- and most of us drive like clones of one another, as we were taught using the same methodology. And, funny, we're always arguing with non double/single clutchers about the pros of doing it (I guess, since it was programmed in to us at the school). I'm always finding myself arguing the same argument. ;)

Cheers.

Yes, the synchros will do the job faster than you if your mash the shifter hard enough. Or you could double clutch, which is not that much more effort, and save your syncros (which are pretty weak on our cars from what I've heard around here... like 2nd gear?).

When you pick double clutching vs simple "heel-toe" you pick which parts you want to save. With double clutch, you are saving the syncros at the expense of the clutch. Whish single clutch, you put less stress on the clutch but more on the syncros. It's up to you really, but a clutch job is slightly less expensive than a transmission rebuild :P

Someone mentioned above that one may be preferable in an enduro race. The syncros working produce friction and _heat_ so I could definitely see how double clutching could help (disclaimer: racing noob)

I snipped everything after this because... well... "duh." Of course you rev match. But if you're double-clutching in a car with a synchro box you are

1) wasting time and
2) putting yourself at risk of making a mistake and wasting more time.

:lol2:

I never said rev matching was a waste of time. I never said running down through each gear was a waste of time. I said double-clutching on a car with a synchro box was a waste of time. Because it is.

I clearly see why it would be perceived as a waste of time (and it clearly can be), yet I do see the value in going through the motions of doing it if one has the opportunity to practice it. It's a good trait to learn- you never know when you'll be asked to drive a stint or two in a dogbox trannied car ;) or if you'll participate in an enduro, lol. Cheers.

I read this the other day and payed attention .. apparently this is a habbit i picked up from my dad ... hahaha who knew!


Rev-matching/heel-toe downshifting - a different technique, which goes like this:
Enter the braking zone and apply the brakes.
Clutch in, shift to lower gear.
Simultaneously roll foot and blip throttle.
Clutch out, engage lower gear.