Blip it!

 

It would be hard to understand why "double clutch'ers were in your rear view mirror", it might be because your and/or your car are fast; but, since you drive a Z it is not likely that you are seeing C6's in your rearview mirror.

But because double clutching is only done when going down one or more gears, it is done under braking as you are entering a corner. Therefore, it does not slow the car down anymore than a regular downshift without a double clutch. In fact, doing a double clutch allows you to change gears a bit faster because the syncros slow down the engagement slightly.

Therefore, I contend that double clutching has little to do with slowing you down on the track. If you are slow you have some other problem. Doubleclutching is optional on the C6 or any other syncro trans car, but a blip in neutral as you change down makes it much smoother. For me, doing a double clutch as I blip is automatic, I have been doing t for years and I can double clutch just about as fast as someone who only blips.

If you want to shift without using the clutch, you can do that, but I would only do it in someone else's car. I learned how to do this by driving rental cars in Europe and it was not easy to do in a consistent fashion. I often grieve about the tranmissions in those poor cars.

 

Excuse my error...when you referred to your car as a "Z", I automatically assumed you were talking Nissan 350Z. I should have known better as you have some nice photos of your car.

 

no it doesnt,

the apparent "1/3 more wear" that you are thinking about would be happening when re engaging the clutch with the shifter in neutral.

clutches wear when they first engage the gearbox's input shaft and transmit the power of the engine to the wheels, where it encounters thousands of pounds od drag ( the weight of the car )

engaging the clutch in neutral for a proper double clutch shift is only engaging the gearboxs input shaft and NOT the rest of the driveline, the drag effect and subsequent wear is EXTREMELY minimal.

the idea that double clutching is an ancient way of shifting is just silly.

look at it like this, if your driving your C6, push the clutch in and ram that sucker from 5th to 2nd your asking the synchros to do a load of work. They have quite some rotation matching to do.

now 20 years down the line when a guy buys his 'classic C6' with a gearbox being treated like this he will find the synchros have had it and he'll HAVE to double clutch to avoid the dreaded GRAUNCH that accompanies stuffed synchros.

if a car is regularly tracked you wont wait twenty years, more like 20 track days before you start noticing a bit of a crunch ( and thats optimistic). i have ALOT of experience with 25 + year old classics with badly treated gearboxes in this regard.

Yes thats what synchros are for and for every day driving they will last a long long time but they will wear out eventually and if your hard driving then double cltuching is the way to go to preserve your box.

also with a properly timed double clutch you will notice the physical act of shifting is incredibly smoother than letting the synchros do it for you and it just FEELS GOOD!

 

The clutch wears every time the clutch disc touches the pressure plate, once when you push the clutch in and again when you let it out. The throwout bearing also wears every time the clutch is engaged/dis-engaged. We're not questioning the rest of the driveline wear, just the clutch.

 

I agree with this 100%. I keep my cars longer than most people, my 911 was sold after 15 years and the C4 was kept for 10 years. I double clutched downshifts 100% of the time on both cars, and the 911 was tracked for years. Never a hint of any clutch or throwout bearing trouble on either car.

I might question BrettC6's example of downshifting from 5th to 2nd, I can't think of any corner I have encountered where I had to go down 3 gears; but, if I if I ever did that a double clutch downshift would be mandatory.

Whether or not to double clutch depends upon one's preference and one's skill. For a lot of people just doing a heel and toe downshift maneuver with just a blip is difficult, adding a double clutch to the mix can be overwhelming, particularily when you are traveling very, very fast.

Clutch wear is a small issue when you consider whether to double clutching or not, if you do it right the clutch engages very smoothly and wear is minimal. As the man said: "It just feels good". Maybe the throwout bearing gets more wear, but regular city driving is probably the biggest killer of clutches and throwout bearings and most of that does not involve double clutching.

 

Just for the record, double clutching and heel & toe are not alternatives: when you heel and toe, you have the choice of whether to double clutch or not. So the decision as to whether you want to double clutch has absolutely nothing to do with heel and toe. Also there are many occasions in day to day driving where you want to change down without braking at the same time.
It's the blipping that's important to the smooth shift, double clutching or not. I have always double clutched while, with Formula 2000, I was asked to do single clutching which, of course, is easier to teach. Choose one or the other but just do it smoothly in either case. Finally, for a really smooth down shift, it's nice to get used to the engine sound for judging the needed increase in rpm for a given shift rather than just crudely blipping the same amount every time.

 

aaahhhh... the sweet sound of performance...

 

good to see someone else is on the ball. my reference to going from 5th to second is more a point of how to wear out synchros. i guess this could happen on the street when deciding to go for a quick blast. though on the track if i come into a second gear corner from a 5th gear straight ill double clutch to 3rd then 2nd.

 

Not 5th to 2nd but i go from 6th to 3rd all the time (same number of gears) when i want to pass someone aggressively on the freeway or when cruising behind them. I double clutch basically all of my downshifts. Do i need to, probably not, but man the cars feels so much better and smoother when i do it. Im only 23 so i never drove a car where i HAD to double clutch but now that i have learned it i will prolly never do a normal downshift again. I like teaching it to my friends as well. It only takes two shifts to convince them, one with a normal downshift and one with a double clutch, it is very easy to tell the double clutch feels much better.

Once you get good, which i feel i have, i can double clutch and downshift just as fast as people downshifting by just blipping the throttle. The key is to just get your left foot moving faster than your hand and right foot, not too hard.

On a related note, i love to do the perfectly matched heel-toe with double clutch coming into a turn man it feels so nice and smooth.

 

I double clutch because it sounds cooler and I think it's neat to see my left leg do the "double twitch". That said, I don't do it for lazy shifts. (Throw the car in neutral and brake down to 15, clutch in, put the car in 2nd and rev engine up then slip clutch out). But when I'm doing 55 mph in 6th gear and see an opening to get past the grandma of the moment, I double-clutch down to third and let the R's fly.

 

Whew. It sounds like you actually know what you're talking about!!

I've attended race schools. Double clutching is good for an 18 wheeler, but totally unnecessary for a sport car. On our F2000 cars we had non-synchro VW trannys - the only necessary action for smooth downshifts was heel and toe. So much for double clutching.

Finally - the braking that is done on a race track is maximum braking just before the corner, and the downshifts are done extremely quickly using heel and toe blips of the throttle. Double clutching would make you extremely slow compared to those actually racing.

 

We have beaten this subject to death and this is my final comment. I don't disagree with anything you have said except for your final comment. In reply to your comment that double clutching "would make you extremely slow", I suggest that you read page 98, the bottom of column 1 of the Skip Barber Racing School book: "Going Faster! Master the Art of Race Driving".

I quote from the book: "Keep in mind that in downshifting there is no lap time advantage in shifting without a clutch." (My comment: same is therefore also true about double clutching vs blipping). "Downshifts come when the car is slowing down and it's the brakes that determine how quickly the car covers this section of the course. Getting the car into the lower gear a tenth of a second faster in competition doesn't necessarily mean that the braking process is going to take a tenth of a second less"

It is all very logical when you think about it.

I guess I also disagree about you comment about "double clutching being total unnecessary in a sports car". I think it is just a matter of driver preference, when you are driving a car with a syncro box you can go either way. I just think and feel that a double clutch is smoother and less hard on the mechanicals.

Incidentally, the Skip Barber book (page 97) estimates that in order to master double clutching so that it is automatic, smooth and instinctive, requires 60,000 heel and toe double clutch downshifts! If that is true there are few people here who know what they are talking about.

 

and this makes it sound like you dont....

ive been racing for 7 years and i double clutch daily and i dont always nail every double clutch shift. i believe your point of view on smoothness would be more akin to a passenger not feeling the shift taking place. from that perspective of smoothness you are correct, a double clutch is not necessary.

what a driver will notice on a double clutch is the act of moving the gearstick actually becomes easier. you wont get the silght binding when changing gears that you do when just depressing the clutch. done right you could change gears with a fingertip.

anybody who can't notice this is not doing it correctly, and until you can do it you shouldnt be making any claims that its useless. once you know how, you'll never shift normally again unless you feel like being lazy (which is me quite a bit)

your point on double clutching slowing you down on a track is also incorrect. if it takes you 4 seconds on the brakes to slow down into a corner then you have 4 seconds to shift. you can do this in half a second or take up all 4 it doesnt matter.

and yes, with that......

 

I just want to make sure I understand double-clutching correctly. Let's say you want to downshift from 5th to 3rd and wish to double-clutch... would the following be the EXACT procedure?

1. Press clutch pedal down, take foot off accelerator simultaneously
2. Shift from 5th to neutral
3. Let up clutch pedal fully, foot still off accelerator
4. Blip throttle (press accelerator down quickly and then let off it)
5. Press clutch down, foot still off accelerator
6. Shift from neutral to 3rd
7. Blip throttle
8. Let up clutch pedal

Please correct whatever may not be dead accurate here. Thanks!

 

If you are running along in 5th gear, and are braking heavily, and are getting ready to downshift, just remember this:

Clutch in.... Move shifter to neutral...Clutch out
Blip
Clutch in.... Move shifter to next gear (go directly to 3rd)...Clutch out

Of course, when you go from 5th to 3rd it is assumed that you are under braking, and the blip is done with the ball of your right foot, while at the same time the right foot is on the brake and the car is at a level of near threshold braking. This is the heel-and-toe maneuver.

If you can already do a regular blip on a downshift while heel-and toeing it is merely a matter of training your left foot to do a little extra action.

Now, on the track you are probably starting all of this action in 5th gear at well over 100 mph, so it has to be automatic, there is no time to think about the shifting sequence because you are shooting for your turn-in point and then the apex, you got a lot of other stuff to think about.

I suggest that if anyone wants to learn the procedure, start at slow speed, i.e. try a double clutch downshift from 4th to 3rd at about 40 mph. Do this a few hundred times at slow speed until you get the basic idea. I have to warn you this is not for everyone, leaning how to double clutch can be a bit tedious, and you have to constantly do it thereafter to maintain your proficiency.

 

Vet
I should have added that your procedure is correct except for that second blip (#7). You just goto 3rd and let out the clutch. Also you are normally under braking while you do all of this.

 

Double clutching a tranny with snychros? You guys should all buy Model T's and then you can manually adjust your ignition timing while you drive!

 

Thanks Dannov!

But wouldn't you still want to match revs for the new lower gear before letting out the clutch? Otherwise the clutch and driveline will experience a good deal of shock and wear. Or perhaps this is just part of the course when racing... a worthy sacrifice in the name of slowing the car down faster? Or are you saying that due to the extreme braking, the revs will almost match naturally without a blip because the speed of the car has dropped so quickly? Again, I just want to make sure I am understanding all this correctly. Thanks for the info!