johnnyg

Down boys! You are both trying to accomplish the same thing, but with different techniques. It's like arguing that dinner tastes better by eating all the meat first, then the vegtables, rather then alternately eating some meat, then some veg.

For my 2 cents worth...has nobody ever NEEDED to get into 1st gear on an autocross course?! I will only say that double clutching sure ain't the answer here!

san7

Wouldn't rev matching be matching engine rpm to tranny input shaft speed, not drive shaft speed. Since the drive shaft is after the gearbox and thus spinning a different rpm?
And I have the same problem with first gear. I use this technique of rev-matching to jam it into first on a real tight corner for killer exit speed.

buttsjim

Maybe it's the terminology here, but Slpin's right--there is a difference between double clutching and rev matching.

Rev matching syncronizes the engine speed to match the speed of the input shaft (which at that moment is being dictated by the rear wheel speed acting through the gears). The idea is to match engine to drivetrain speed to enable smooth driving.

With double clutching you shift from one gear to neutral, disengaging the input shaft from the rear wheels. Then you let out the clutch (which engages the input shaft to the engine) and rev the engine (and input shaft) to the proper speed. Then, you quickly shift from neutral to the next lower gear before the revs drop back down. Double clutching is the classic trucker (and old time racers') technigue to enable down shifting without syncros. It is a similar, but different technique from rev matching.

I think the distinction has been lost over the years, but there is a difference.

RETed

Nah, you're right.
You gotta excuse the loss of detail.
I type my replies in the middle of 16 hours of work.
Even when I'm not at work, it's in the middle of my 8 hour "break" in between work days.


-Ted

RETed

I always thought double clutching was rev matching?
"Rev matching" is a generic term, while "double clutching" described a specific way to rev match?


-Ted

kick7ca

If you can downshift and match revs with a throttle blip while at the same time braking, then your a real shooter.

I downshift to now and again if coasting slowly enough in 2nd where 1st would give me about 3-4000 rpm, with a good throttle blip ofcourse.

buttsjim

Yeah, double clutching is a form of rev matching, but it's more than just blipping the throttle. You literally do "double clutch"--once from the higher gear to neutral, and then again from neutral to the lower gear--in an attempt to get your transmission internals all rotating at the same speed. True double clutching was the method used before syncros, for the same purpose that syncros now perform. So, if your syncros are broke, true double clutching would be the ideal method.

I'll confess, this is so clear to me due to my age. I was a teenage driver in the mid-sixties, when we all had American cars with 3-speed on the columns. Since first gear wasn't synchronized in those transimissions, the true test of manhood was being able to consistently downshift into first at 30 MPH without graunching the gears. Blipping the throttle to rev match wouldn't get it done. Double clutching would.

buttsjim

Sorry, I need to correct a mis-statement I made in the second paragraph of the previous post.

The TRUE test of manhood for a sixteen year old in the sixties was being able to prove you weren't a virgin. Next, was to be able to chug-a-lug a beer in 6 seconds or less. Next, was to be able to open a bottle of beer with your teeth. THEN came being able to double clutch into first gear. Sorry for the confusion.

johnnyg

Geez, it's a damn good thing I was 16 in the 80's

MARTIN

the point that I was trying to make, was that you dont need to use the clutch for anything other than starting off.. Downshifting/upshifting can be done by just leaving the clutch engaged. I do it all the time. No need to go through all that trouble of "double clutching and what not to accomplish the same thing".

buttsjim

I agree with that (except it's hard on the car when you don't get it right). I jumped in the discussion to clear up the smoke between double clutching and rev-matching. I quoted the wrong post before making my point.

And you reminded me of yet another test of manhood. Shifting without a clutch was number 7, right after having your own (not your parents' car), and just before rolling said car on your local "dead man's curve".

slpin

iTrader: (9)

this is what i mean

http://www.boostaholic.com/revmatching.html

obviously, you guys cant even understand the difference between rev match, double clutch.... and you are bringing in shift without clutch in to something completely unrelated....


i am saying... if he cant get it into the gear at speed, double clutching will allow him to shift into the lower gears easily... if his transmission is fucked, it will let him use it longer... but all rev matching is, is matching the driveshaft speed, and how would that allow him get into the gear if his trans wont let him?

I Hate Ricers

Well said Slpin. If everyone on the forum drove a car that had bad synchros, we would all know the difference between rev-matching and double-clutching.

And damn that Fast and the Furious, "Not double clutching like you should..."
Just adds to the confusion. I've heard kids calling clutch kicking in a race to get the rpm up in first gear "double clutching". Sheesh!

2slow4stock

iTrader: (18)

Yeah, but clutch kicking is just dropping the clutch which on a very dry day can mess up your drivetrain. Which is a no no. Fast and the Furious is all non-sence with sexy cars, but just something to watch and make fun of since they don't know that were talking about.

MARTIN

Heres what Im saying..double clutching is basically accomplishing the same thing as not using the clutch to engage/disengage gears... with the clutch engaged, the input shaft is always spinning at the speed of the engine, and therefor by not using the clutch, there is not use for the syncros...

while in neutral(leaving the clutch engaged) you higher or lower the rev depending on which gear you want and just slide in to your gear. Its the same ****, but double clutching is 20 times more complicated.


There is no need to engage the clutch, rev, disengage, select gear and engage again... All you really have to do, while leaving the clutch engaged(forget about the clutch pedal), is rev to w.e. gear you need and slide the lever in, simple as that..

RETed

Not exactly what I do...

1) Clutch in
2) Rev engine with gas pedal to match engine RPM's to trans
3) Shift lever should drop right in - you only need slight pressure to get this to work, if done right
4) Clutch out

So what's the difference?
My method is like a lazy double-clutch.


-Ted

I Hate Ricers

You are rev matching right there Ted. That slight pressure you are talking about is the synchros doing their work. Rev matching will ease the wear from down shifting on your clutch disk, but it won't really help your synchros out. Most race drivers will either rev match, or double clutch (and rev match as well). If your synchros can handle the abuse of fast down shifts, then so be it. If your tranny had poor synchros, then that "slight pressure" would be more of a "slight crunching sensation" as your gears are forced to mesh.

Double clutching isn't really a necesity, I mean, modern cars are designed to be shifted normally. However, as our cars age, our synchros aren't always going to be in the best shape. Double clutching can prevent excessive wear on the snychronizers. It is a technique that takes time to learn and do...theoretically it should take more time on the race track to complete a proper downshift-double clutch-rev match than simply downshifting, but if you don't have a sponsored car, you better learn it!

Also, if you double clutch and rev match you should feel *NO* pressure as the gear shift lever slides right into place. With time and practice, even fast shifts will slide in with no resistance (b/c the synchros don't have to do anything remember?). You will have to blip the throttle twice to do it right...and i'm not gonna right out the whole procedure

@MARTIN

I know what you are talking about, I used to practice clutchless shifts on an old pick up truck just for fun. If you can shift all of the time w/o the clutch than you have a lot of skill. But I wouldn't call it "double clutching"....if you don't even use the clutch! And I don't think advocating to the masses on this forum to do clutchless shifting is the best idea, do you?

Anyone that wants to learn proper double clutching, I would suggest finding a friend or car geek that knows his/her stuff to show you in person. It is too easy to get the wrong idea from some guide on the internet or a *gasp* forum. If you do it wrong but think you do it right, you can develop some nasty habits that might put more wear on your synchros thatn doing nothing at all.

One last thing, my 58 year old father, has been driving a 1987 Alfa Romoe milano with a crappy tranny that is known to break and need repairs <30K for 250K miles on the original clutch disk and synchros. How? Proper double clutching and rev matching in daily driving. The benefits of learning properly are there for sure.

Hope that helps!

RETed

Hmmm...that was kinda vague. :P

I meant that I just need to put very little pressure with just two fingers to get the trans to shift when rev matching my way.
I run a Razo (RA3) that shortens the throw, but this also amplifies any "feedback" through the transmission cause of the shortened leverage.
I wasn't talking about pressure from the trans trying to "fight" the shift itself - that's obviously the synchros trying to do their job.
I know all about trying to "bang gears"; I used to drag race the FC for a while, and that 1st to 2nd shift at redline used to fight all the time!

Well, I think the discussion is going around circles at this point.
The goal is still to get the engine RPM's to match the RPM's the transmission is spinning at a certain vehicle speed.
The "transmission" implies the rear wheel / rear diff / driveshaft rotations, since you cannot decouple any of that. :P
The only think you can decouple is the clutch.
So...it's still a matter of matching engine rotations to clutch / trans rotations, right?


-Ted

buttsjim

Well, I think you're right in that the discussion is going in circles, but we may as well go ahead and beat the point to death.

I quoted your statement above because that's the difference between rev matching and double clutching. Rev matching matches ENGINE speed to road speed (as seen at the input shaft). Double clutching matches the drive/driven gear speeds WITHIN the transmission.

As stated, double clutching isn't necessary with modern syncros, and the method you described works perfectly okay. Except for first gear, I do it the same way as you. However, if you encounter a transmission with broken or non-existing syncros, double-clutching is the way to go.

RETed

Ok, now I get it...
It's the clutch, shift in neutral, clutch part that does the trans input to trans output matching, right???
Yeah, now I see your point.

The starting point and ending point is the same for all of this.
Double-clutching adds that extra step for what you described.

Does that make sense now?


-Ted

buttsjim

Yep. Makes sense!

MARTIN

W.e., yea I get what you people are saying in that its difficult to do and what not and it does take some practice... Anyways, clutchless shifting is in essence the same as double clutching, since botch accomplish the same goals.. But I will remove myself from this thread since the answer has been posted over and over again and all we are doing is going back and forth.