dsmith

Z-Man and Larry have hit the high points, so in summary:
To minimize lap times you have to be proficient in heel/toe downshifting. Any other technique wastes time in coasting, as pointed out, and potentially unsettles the car. Lots of books on the subject. Easy to learn, hard to perfect and absolutely a necessary race driving skill.

You don't have to be at maximum braking to learn it. In fact, professional race schools have students drive in slow circles shifting between 1st and 2nd to learn. You can learn on the street any time you are going to accelerate after the downshift, like around a turn onto a side street, or just coming down to a slower speed, like an off ramp.

For students who can't heel/toe, I force them to complete their downshift at the end of braking before applying throttle again (no clutch use or touching the shifter before the actual shift). It lets me know they are conscious of what they are doing, keeps focus on the braking zone and turn in, and minimizes drivetrain lock up/spins and component damage.

I don't bother with doube de-clutching, except on the street from 2nd to 1st.
David

TD in DC

To me, this is the key. My instinct, and I think the instinct of many other street drivers is to let the clutch out slowly, which lets the revs drop too low. A strong blip with rapid release of clutch keeps the drivetrain engaged and smooth.

racer

Well, not if they have a sequential shift car

I think it should be pointed out that the double de-clutching is a perfectly fine technique, although it isn't really necessary given modern transmission designs (like syncronizers and curved gears). In the early racing days or with any manual transmission that had no synchros, double-declutching was the norm.

It may also have been more practical as a way to help slow an early car down from speed by "going thru the gears" ala 5-4-3 instead of a straight 5-3 downshift. Old cars had worse brakes than transmissions for the most part. Today's modern (powerful) brake systems they have made the transmissions the weaker links and the part worth NOT using to help slow a car from speed.

Veloce Raptor

IMNSHO, this is a BIG mistake. It is far smarter to run thru the gears sequentially. Hell, in modern synchro cars, that should be a breeze. For instance, at Road Atlanta, in a GT3, coming down the back straight I am at the top of 5th gear at 155+ MPH, and I need to get to 2nd gear for T10A. I do NOT go 5th to 2nd. I go 5-4-3-2 in less than a second, and thus am 100% certain of what gear I am in.

tkerrmd

Well if the 4 to 2 is Ok with Carroll Smith I dont feel so bad, thanks Brandon.

Larry, I took the car in after your comment on the LWFW and the dealer said there was a problem with the throttle body and ECU software and then corrected it!! So thank you for pointing out that my occassional stall was not the LWFW as I had been told before!!! Now car better than ever, you are a genius!!! thanks tom

Andrew you are certainly every bit as fast as I at Sebring, I just try to stay out of the way!!

Veloce, at Road Atlanta I too am in 5th and over 150mph but I have to admit I drive into the break zone in 5th threshold brake heel toe to second and go. Not sure if I could ever phyiscally do as you with the 5-4-3-2 in a second!!!! Do you actually re-engage the clutch fully between each shift and all this is in the brake zone? I just realized I really dont know how to drive now, damn!!!!!

Veloce Raptor

No, I only partly re-engage the clutch, just until I feel it begin to grab, then I disengage it again for the next shift. I only fully re-engage it when I reach 2nd gear.

TD in DC

Why? What does this do?

Honest question. It would seem to me that unless you fully re-engage the clutch you are not getting any benefit by going through the gears apart from making certain that the shift lever is in the proper physical position (so that you don't money shift or so that you will be ready to go if you need to get back on the gas before completing the full extent of your downshift). If this is true, then it wouldn't matter what you did with the clutch at all (you could just leave it pressed in for the entire rowing period provided that you just make the throttle blip at the end when you go from third to second).

What am I missing?

Veloce Raptor

Mostly, it is force of habit & making sure I am in the proper gear. However, by re-engaging the clutch part way, I am also bringing driveline bits up to wheel speed, in case something dire happens & my foot slips off the brake or something...to prevent massive rear lock up.

TD in DC

Bear with me here, because I really am trying to learn, but is it really true that you can actually bring the diveline bits up to wheel speed without fully releasing the clutch? Is it possible that partial reengagement merely decreases, rather than eliminates, the speed differential? If this is true, it might lessen, but not prevent, rear lock up in the event something massive happens, right?

Mike Murphy

I don't think you even need to let the clutch out at all in order to bring "some" of the gears up to speed. The clutch only engages the engine, but the other bits are always connected. So, cycling through the gears, regardless of clutch will bring the bits up to speed. I find it easier, for example, to go from 3,2,1 when the transmission is cold than going from 3,1.

TD in DC

Are you sure about that? That is not how I understand things to work, but I have been known to operate under a misunderstanding once in awhile.

In reality, there are two totally different things going on here.

One is easing the ability of shifting, which is only accomplished by double-clutching. When you double clutch, you make it easier to shift when you put the car in neutral, blip the throttle, and then shift into the lower gear at the point that the rpms are synched. I understand that this is no longer necessary with modern transmissions.

The other is to ensure that your wheel does not lock up when you release the clutch, which you accomplish by rev matching. When you are rev matching, you do not need to have the car in neutral . . . you just need to have the clutch pedal depressed. So long as the rpms of the motor exceed the rpms correlating to the rotation of the wheel in the relevant gear at the moment the clutch pedal is released, then the wheel will not chirp. If the RPMs are below the RPMs that correspond to the wheel rotation speed in the relevant gear, the wheel will chirp when the clutch pedal is released.

I think Dave is talking about the latter, not the former, which is why I am confused.

Mike Murphy

Well, I've had a Muncie M40 transmission apart from my 68 Chevy Nova. I was a little surprised to learn that the gears are always connected to each other inside the transmission. All of the gears, in fact, except for reverse gear. They are direct-connected to the drive shaft. So even with the car in neutral, and the engine off, and with the clutch in, if you have a buddy push the car down the road, all the gears in the transmission will spin!

Veloce Raptor

Agreed.

They are, in truth, not fully to speed, but IMO probably 3/4 there, based on the amount I am engaging the clutch.

Larry Herman

The clutch "connects" the motor to the input shaft. The input shaft is locked to the slider sleeves. The selected gear is connected to the input shaft by the slider sleeve and the "dogteeth" on that gear. It is in constant mesh with its mate on the output shaft. All the gears are locked to the output shaft which drives the R&P. Simple right?

If you keep the clutch depressed, you can speed up the clutch disk by shifting down through the gears. The syncros will speed up the input shaft. At some point, you must blip the motor to get the flywheel/pressure plate assembly up to the speed of the clutch disk so that you get a smooth re-connection of the motor to the drivetrain.

Greg Fishman

Watch Leh Keen's video. He goes through all the gears. Other pro drivers I have ridden with do that also.