Looks like I came across this thread a little late (Still confuse..., Please help me double-clutch properly) and it has since been closed and ended like this...
I did have one additional contribution that might be considered useful. It will perhaps change the way some of you, as competition drivers, see double-clutching. I hear and read a lot of opinions on how double-clutching is an extra step, a time waster and an addition of complexity that doesn't belong on the racetrack.

Typically, those types of comments come from people that look at the act of downshifting as a number of serial steps. The original poster in that other thread broke it out something like this...

1. brake
2. clutch in
3. shift to neutral
4. clutch out
5. blip throttle
6. clutch back in
7. select next lower gear
8. clutch back out
9. off brakes

That's a daunting number of steps. However, that's not how our bodies actually work on a regular basis. This type of serial processing is accurate when you are thinking about an action consciously, when you are just learning something. But when you have already learned something and brain processes it subconciously, your body can parallel process and do quite complicated things. Take walking for instance. Try and figure out all the steps required to walk down a hallway. There are so many it would be overwhelming and we'd probably decide to just stay on the couch (or not attempt to double-clutch, in this case).

So, when you consider how double-clutching works when your body processes in parallel, it isn't any slower. Really. The reason is, you are not actually going through the 9 steps listed above. Things are going in that order, but actions are happening in parallel.

There are three ballistic actions that occur during a double-clutch. A ballistic action is an action that your brain starts, but doesn't have to finish because your body is programmed to complete the series of actions. Here are the three actions my body performs when I double-clutch. These are not in order, they are parallel processes that are synchronized appropriately.

1. Right foot depresses brake, throws in a throttle blip at some point and comes off the brakes later.
2. Right hand moves shift lever to neutral, then to next lower gear.
3. Left foot pumps clutch twice quickly

So, when you think about the body's ability to parallel process, it becomes a much simpler task of performing three synchronized actions simultaneously rather than performing nine separate actions serially.

To show how a double-clutch is no slower than a single-clutch, let's look at what happens during a single-clutch:

1. Right foot depresses brake, throws in a throttle blip at some point and comes off the brake later.
2. Right hand moves shift lever to neutral, then to next lower gear.
3. Left foot pushes clutch down for the duration of (2) above.

So the only difference between the two is the left foot pumps the clutch twice quickly instead of holding the clutch down for a longer single cycle. The KEY here is that there is no pause while the shift lever is in neutral. As the shift lever is passing through neutral, the clutch is already out and the throttle has been blipped. No extra time was used.

Consider these three parallel processes (rather than nine individual steps) and watch the video again. It's clear that there are three processes taking place that are just tightly synchronized. Footbox Video

Does that help explain it?

The point of this post isn't to change anyone's mind about the benefits (or lack there-of) of double-clutching. It is to show that there really isn't much difference at all from a driver point of view between a double-clutch and a single-clutch downshift. It takes no additional time and once it's learned, takes no additional effort.

I double-clutch my downshifts because it is easier on the synchros and actually makes the engagement to the next lower gear easier (less arm effort). Any time I can have some mechanical empathy for the racecar without sacrificing laptime, I do it. Nostalgia and truck driving have nothing to do with it.

Double-clutching isn't necessary and isn't going to reduce your laptimes. It's also not difficult, it's not pointless and shouldn't be dismissed out of hand.

Gary
Sheehan Motor Racing
www.garysheehan.com

 

Well-put! Thanks for taking the time to lay it out so clearly.

I don't see how anyone can argue against the fact that it takes no additional time, and only marginally more effort, and is easier on the car.

 

Thanks for the explanation. Makes sense.

 

Well, the argument is valid. That extra effort and ease on the running gear isn't absolutely necessary. The benefits are small and perhaps not worth the effort required to change how they drive.

Gary
Sheehan Motor Racing
www.garysheehan.com

 

Are you bored Gary?



(Ry)

 

[QUOTE=krazik,Jan 7 2008, 12:09 PM]Are you bored Gary?

 

That was the last time I was at the track w/ the race car. Car is down for the winter.

 

Good summary. I never tried double-clutching since I thought I'd take more time than single-clutching, but your point about quickly pumping the clutch twice makes sense. I'll try it on the way home tonight.

 

Hey Gary.
I didn't even know you were in here.
very well put and sorry your sick at home.
James

 

How to downshift:


1) Brake
2) Clutch in
3) Blip
3.1) Downshift
4) Clutch out


Double-clutching is absolutely unnecessary with today's synchro'd and dog-ring'd gearboxes. Take a poll of the GrandAm field at Daytona and see how many of them double-clutch. It does have an affect on lap time.