Heel-and-toe double-clutch downshift08:43:58 AMHeel-and-toe double-clutch downshift. For those of us with manual transmission cars, this is just about as good as it gets when it comes to shifting. The thing is, most people have never even heard of it. Of those who have, a lot still can't do it.
Just this morning, I was reading an article in AutoWeek about several NASCAR drivers who recently spent a couple of 
days at the Bob Bondurant School of High Performance Driving trying to learn more about road racing. As opposed to their usual roundy-round racing.
The comments which surprised me were along the lines of, "I'm getting the hang of it, but the footwork is a lot different...I'm gonna have to go home and buy a cheap car with a manual transmission so I can practice on this." Maybe it's not so surprising; there aren't many NASCAR races where those guys--many of whom are great drivers--have to downshift, except when they're coming into the pits. It's not an important skill to them.
But to road racers and, I venture to suggest, many enthusiasts, it is an important skill. So what is it I'm talking about? I'll tell you...
In a response to a question to one of my other blog rants, I explained how heel-and-toe downshifting works. You can read that post if you like, but the short version of the story is this:
It's quite possible in most cars to operate the brake and throttle at the same time, with the same foot. If you do it right, you can blip the throttle to get the engine up to the correct speed for a smooth downshift while, at the same time, braking for, say, a corner.
This technique is called heel-and-toe downshifting even though it's usually done with the sides of the foot. Left on the brake, right on the gas. It sounds a bit reckless, like inviting unintended acceleration or something, but in practice it's really quite easy to do. More importantly, it makes your downshifts much smoother (at least once you can do it consistently), upsets the car less, and doesn't jerk around your passengers.
But, while heel-and-toe is good, heel-and-toe with a double-clutch downshift is even better. What is that, you ask? Let me explain:
The point of doing any of this is to ease the transition as you go down through the gears. That is, to match the engine's revs up with what they'll need to be for a new, lower, gear. If I'm at 4,000 RPM in fourth gear and downshift to third, the revs will rise to about 5,000 RPM. Everybody knows that.
During that downshift, I take my foot off the accelerator and push in the clutch so I can shift. The engine, which has been clipping along at 4,000 RPM, suddenly returns to idle (1,000 RPM or so) since the clutch is disengaged and you aren't pressing on the gas. To the engine, this is really no different than sitting at a stop light.
But then you engage third and let out the clutch. Either you let the clutch out quickly and give the car a big jerk, OR you slowly eaaaaaaase the clutch back in and let the gradual engagement of the clutch and the turning of the tires pull the engine back up to 5,000 RPM or so. While this works, it's both (a) slow and (b) hard on the clutch because you're making it slip all the time it's coming back up to speed.
Heel-and-toe gives you a way to get the engine up to the right speed without having to drag it there: You simply blip the throttle and then let out the clutch while the engine is still at more or less the right speed. Much faster and smoother. And easier on the drivetrain.
But simply heel-and-toeing, while it does get the engine up to speed, does nothing for the parts of the transmission that need to come up to speed. For that you need the double-clutch.
If you think about a manual transmission, there are kind of two sides to it. There's the input side which is connected to the engine (through the clutch), and the output side which is connected to the driving wheels through some kind of driveshaft (OK, not all cars have driveshafts, but go with me on this). Connecting these two sides are the gears.
If the car is in neutral, the two sides have no connection to one another. Each can do its own thing because, well, that's what neutral is. Assuming the clutch is engaged (that is, your foot is off the pedal), the input (engine) side is turning at whatever speed the engine is turning. Similarly, the output side will be turning at the same speed as the driveshaft. If the car is sitting still, the output side (and the driveshaft) aren't moving at all.
If you're in gear and moving, the two sides are connected by gears and turn in some ratio to one another. In lower gears, the engine side turns much faster in relation to the output side than it does in higher gears. In a Porsche GT3, for instance, first gear has a ratio of 3.82 to 1 (meaning it takes 3.82 revolutions of the engine to turn the output shaft one full revolution) while 5th is a direct-drive 1.00 to 1, meaning both the engine and output sides are turning at the same speed.
Unrelated to this conversation but for what it's worth, you've probably heard of overdrive transmissions. Technically, overdrive is related to the gears, not the transmission. Sixth gear in the GT3 is an overdrive gear, with a ratio of 0.85 to 1, meaning the output shaft rotates faster than the engine. It's not just driven, it is overdriven; being made to go faster than its power source.
But I digress.
Let's say you're in the GT3 (I wish), in 5th gear, at 4,000 RPM. The engine is turning 4,000 RPM, the engine side of the transmission is turning 4,000 RPM and the output side is, too, because it's a direct-drive 1.00 : 1 transmission. Everything is going the same speed.
But then you put in the clutch.
If you've left the car in gear, everything in the transmission continues along at 4,000 RPM because the input side is being driven by engaged gears which are being driven by the output side which is, itself, being driven by the wheels. That's just fine.
But when you put it into neutral--when you go from 5th to 4th, for instance--suddenly there's no drive to the input side from anyplace. So it starts to slow down. OK, it's not a lot but it happens. More to the point, what you really need it to do is speed up because 4,000 RPM in 5th is the same as 4,840 RPM in 4th in the GT3. That's where you really want it to be.
If there were no such thing as synchromesh transmissions, to downshift without crunching, you'd need to match the revs on the two sides of the transmission before shifting, whether up or down. Thanks to Herr Dr. Porsche, this isn't really necessary. Modern transmissions have synchronizers in them, which use friction to essentially match revs inside the transmission. But the thing is, it takes time. Not a lot of time, but time. So it slows down your shifting a teench.
Enter double-clutching.
If, while your car was in neutral, you were to re-engage the clutch (take your foot off it) and blip the throttle, you would speed up the input side of the transmission. And, if at the moment it got to, say, 5,000 RPM you disengaged the clutch, and quickly put it into 4th gear, there would be little if any need for the synchronizers to drag it up to speed.
That would make for a faster and smoother downshift from the perspective of the transmission internals (and from the perspective of your shifting hand).
The thing is, did you notice the "blip" in that sentence? That's the same blip as in the heel-and-toe technique. At the same time it's speeding up the transmission to the right point, it's speeding up the engine to the right point, too, since the input shaft and the engine need to turn at the same speed.
Aren't racers clever?
So, a heel-and-toe, double-clutch downshift goes like this:
- Brake with the left side of your (right) foot.
- While still braking, depress the clutch and move the shifter to neutral.
- Release the clutch, blip the throttle with the right side of your (right) foot, then depress the clutch again.
- Move the shifter into the next gear and release the clutch.
- Repeat as necessary until you're down to the correct gear and it's time to quit braking.
It sounds horribly complicated and ridiculously slow, I'll admit. And, there's no getting around the fact it takes some time and practice to get right. But the truth of the matter is it's not very hard to do and is very fast. You can downshift much more quickly this way than using any other technique I know of.
Best of all, once you learn how to do it, driving a manual-transmission car is just that little bit sweeter. And, what's bad about that?
1. Stan Rogers01/07/2005 02:53:09 PM
Homepage: http://stanrogers.blogspot.com
Ahh, clutches are fer stoplights -- if your throttle work's good you can use two feet and just yank it in and out of gear (rally driver; Datsun 510 w/crashbox, late '70s vintage).
2. Scott Good01/07/2005 03:28:19 PM
Homepage: http://www.scottgood.com
That's true. My Formula Atlantic car had dog gears (no synchronizers, very fast engagement) and I did just what you're saying: Used the left foot for braking and did double-clutch downshifts sans clutch. It worked a lot better than it should have!
3. Stan Rogers01/07/2005 04:06:06 PM
Homepage: http://stanrogers.blogspot.com
I meant to ask -- how on earth did you do FA? My glasses made my nose hurt around corners in Super Vee after a few laps.
4. Scott Good01/07/2005 04:42:38 PM
Homepage: http://www.scottgood.com
I actually had a Super Vee, too (1985 Ralt RT5). In 1990, when they got rid of the Pro Super Vee series they added Super Vees to the Formula Atlantic class. More downforce, less power, less tires.
At the Pro Atlantic level it wouldn't've had a chance (not that it was eligible), and was an underdog in Nationals, but in Regional races I could usually put it on the front row. In 1992 they allowed the engines to go from 1600 to about 1800cc, which would have evened things up nicely except that's when I ran out of money and gave it up (there were Visa and MasterCard decals on my car, not because they were sponsoring me but because I was using them to pay for most of it).
As to the glasses, I usually wore contacts. With glasses my eyes watered too much from the wind, and the bumps would make them wiggle, messing up my vision. Plus, contacts mean no sweat dripping down the lenses!
5. Stan Rogers01/07/2005 04:53:01 PM
Homepage: http://stanrogers.blogspot.com
Believe me, I GET the money thing. My rally banger was a 510 not because I always wanted a Bluebird, but because I could put one on the road with spares for eight grand and pass inspection anywhere, and my formula rides were weekend rentals (even the first non-super Vee I drove). Must be nice to be contact-tolerant -- I had to get used to the cinema-verite camera effects view of the world. Usually, if you aimed for the middle apex, you could stay on the road. Usually.
6. Max Leasing05/01/2007 11:42:21 AM
Homepage: http://www.selectalease.com/reviews/mini.html
Cheers for a great article, I am trying to get to grips with the heal-toe breaking. It's getting easier but still have a long road ahead till I can master it.
7. Richard Gaster kirunda-kampala, uganda.02/21/2009 02:28:20 PM
Homepage: http://www.yahoo.com
Great article, now icruise like atypical rally ace with heel and toe double clutching technics!
8. Richard Gaster kirunda-kampala, uganda.02/21/2009 02:33:19 PM
Homepage: http://www.yahoo.com
Great article, now icruise like atypical rally ace with heel and toe double clutching technics!<b></b>
9. barry richards01/06/2011 03:39:07 AM
Homepage: http://contactlensesmall.com/PureVision/
nice article about heal-toe breaking.
