oo7arkman

iTrader: (2)

I was doing some browsing and ran across this. I have seen a lot of questions on here about double-clutching/ heel-toe downshifting and I thought some people are as visual as I am. First a written explanation of technique:
1) Let off the throttle, press in the clutch, and shift the into neutral.
2) Let out the clutch.
3) Bump the throttle to make the engine rev
4) Press in the clutch.
5) As the engine speed decreases to match the transmission speed, throw the stick into the next lower gear. Since you actively matched the revs, it should fall right into gear.
6) Let out the clutch. The downshift should have be very smooth.

Now a link for the video: http://www.youtube.com/watch?v=0j-3xIZK-Bk

Infini IV

^^ Heel-Toe downshifting is more closely related to Double-DEclutching

Double-clutch is a term referred to up-shifting, and most often done with old, non-synchromesh transmissions. To shift up, you would clutch in, pull it out of gear and clutch out... then clutch in and blip throttle, shift up, then clutch out.

wrankin

I double clutch upshifting into 5th on the FD. They synchros are going and it definitely keeps the "crunching" down.

jimeby

iTrader: (1)

Double clutching refers to either an upshift or a downshift.
Heal and toe refers to double clutching while simulatiously using the brake.
Here's a good description of double clutching.
http://en.wikipedia.org/wiki/Double_clutch

DigDug

Heel-toe and double clutching are two completely separate things. Heel-toe is just a technique to blip the throttle while braking to match revs on downshifts. Double clutching gets the shaft and gear speeds closer to synchronized before engaging a gear. You can heel-toe to blip the throttle while double-clutching, but they're not really related.

ptrhahn

iTrader: (9)

^^^^

That video is the way I learned it at Skip Barber, and the way I still do it today with the synchro'd RX7. I know I don't have to, but since it's a rhythm operation, I wanted to have the technique in case I ever drovbe open wheel again.

FWIW, they referred to it as "double de-clutching" in contrast to "double-clutching", which I used to have to do with the old International deisel moving trucks. :-)

Roen

iTrader: (2)

heel-toe and double-clutching are unrelated.......I only double-clutch heel-toe just for kicks.

The rest of my heel-toe downshifting is only done with one clutch motion.

oo7arkman

iTrader: (2)

I agree. And regardless of whether you are double clutching a shift in either direction the technique is the same, the difference is only if you are up-shifting or down-shifting.

I just thought this video was a good visual example of double-clutching (or double DEclutching in this particular case) as well as heel-toe driving as well. Yes, they are two separate techniques but often employed together.

maz-rx

"Double clutching" or "Doulbe de-clutching" is as stated used for cars without synchromesh gearing known as a crash gearbox (not including dog engagement) and is not needed on any car of about the last 40 years. So it is totally pointless and slows you down.

"Heal-toe" is used as stated while braking. You brake put in the clutch and with that held in, rock your foot to the gas pedal to raise the rpm before selecting the lower gear. If you get it dead right the blip should get the rpm to level it will be when you select the lower gear and release. If your driving fast its alomost a necessity as shifting down can cause the rear wheels to lock up on the downshift and cause a spin, this is how the "shift lock" works in drifting.

I tend to "heal-toe" most of the time as it helps to releave the stress on the gearbox.

ptrhahn

iTrader: (9)

Just a bit of a fine point... there's no reason that double-declutching (downshifting) necessarily "slows you down"... the time you have to downshift is typically governed by the time you have under braking. So long as you're thresholding braking, you could be quadruple declutching (if there was such a thing), and it wouldn't lose you any time.

The reason it's done in a non-synchro box is because of the wheel lock issue you describe, which would occur even if you rev-matched with the throttle on a single declutch. The double declutch is "pointless" on any modern road car, but it isn't necessarily pointless for you, the driver, if you wish to ever drive anything but a road car on track.

Upshifting is another matter, but I don't think anyone double-cluch upshifts, even in non-synchro race boxes.

designfreak

Im a little confused over the idea of blipping during an upshift. Are you doing this to match the tranny input/ output shaft speeds up to account for the lower revs in the next gear? Normally just the pause time inbetween shifts is enough to let engine speed drop slightly and match the output shaft speed without upsetting anything. In any case it should be easier to engage the gear with the the input shaft spinning higher than the output ( engine rpm higher than driveshaft rpm) than viceversa as during a downshift.

What am I missing here?

On a sidenote I noticed Steve McQueen doing this with the mustang in the chase scene in Bullitt, and I always thought that he was crazy for it, I guess maybe he had a reason...

Roen

iTrader: (2)

If you don't upshift fast enough and the revs drop below the point for the next gear, you'll have to blip. I think that's what the previous poster was getting at......

jimeby

iTrader: (1)

I believe the double clutch is very useful. Our car, like many other club racers uses a (ahem) less than fresh stock transmission. When running a 25 minute race, the transmission and oil become well overheated and the older syncronizers are not as willing to speed up the gearset when shifting. In addition, we downshift from the gear we enter the corner into the gear we wish to use to exit the corner. So for example, we downshift from 5th to 3rd or 4th to 2nd. So, this means the gear set has to make a big change in speed. In this scenario, the double clutch is very helpful.
For our upshifts, we just push in the clutch, move the lever to neutral, hesitate a second, put in next gear.
I have some windshield cam videos posted under username j1m3by on utube (shameless plug) you can't see the fancy footwork but you can at least see the results of it.

Roen

iTrader: (2)

Maybe it's my personal preference but I rarely rarely do 5-3 or 4-2 shifts. I usually brake, downshift, brake some more, downshift again, e.g. 5-4-3 or 4-3-2.

I've never had to double clutch during a 25 minute session either....

Mahjik

iTrader: (1)

I do. Only because the E46 M3 gearbox sucks during the winter and that's the only way I can use 1st, 2nd and 3rd until the car warms up.

maz-rx

It does slow you down as you dont only use the brakes to slow you, you also use the natural engine braking effect and while your double clutching your not doing this. Double clutching does indeed help prevent the rears from locking but only because your doing a long version of heal toeing!! Also if your relying on just your brakes slowing you down you are unnecisarily heating them up, and then you can say hello to the wonderful world of brake fade

If you driving a REAL race car as you put it, it wouldn`t use syncros anyway it would have straight cut gears working off a dog engagement and this again does not need double clutching but it will stillneed heel toe to prevent lock rear wheels again!!!!

I stand by my comment that double clutching is pointless

and by the way I have a degree in motorsports engineering and currently a race engineer on a Porsche 996 bi turbo (A "REAL" race car) so do know what I`m talking about

maz-rx

Most people will rarely go 5 - 3 etc as with missing a gear like this on track looses you time as your missing using that gear for engine braking even if it is only for a very short time, you also risk over revving the engine if you don`t get it right. But this is more down to personal preference really. On a sequential system you can`t miss a gear anyway.

designfreak

I know many schools including skippy teach gear skipping, but I dont do it. I row throught the gears, and I do a full double clutch each downshift. If you do it proficientlly I dont think you will lose any time over just rev matching with the clutch in, and It will be much friendlier on the gearbox and clutch. In club racing where the team budget comes out of your bank account (especially) I think that maximum mechanical empathy is the way to go.

I've read various pro drivers say this about downshifting, and it is the truth with me...the double clutching and sequential downshifting serves as rhythm and preparation for me going into a corner. When I'm teased by the idea of skipping gears I feel that my rhythm gets all messed up.

ptrhahn

iTrader: (9)

Your qualifications notwithstanding, "engine braking" was largely necesarary when brakes used to be terrible, i.e.: wouldn't last a whole race or even a whole lap. I've not heard of too many modern racecars requiring braking assistance from the engine to avoid fading... and mine certainly don't have that problem.

kenn_chan

sorry not to be an ***, but have you won every single race you have entered? No? then you might be right, but until you win every single race you enter, then you are not necesarily right 100% of the time.

I know plenty of people who run REAL race cars, and are totally full of ****, and as often as not finish fairly low in the standings.......

just a thought.

kenn

maz-rx

Looking at the data analysis of good and not so good drivers and styles you can tell.

Our team has won the super sport class twice, and finished 5th in the second year of the GT class in the Supercar Challenge so we`re not too bad. I`m not a driver I`m a race engineer (although I am driver for fun soon entering TA club in the UK) as a race engineer I know for a fact double clutching is unnecisary but heel toeing is necissary.

I`m not going to get in a big argument, lets just agree to disagree (although, I`m right )

p.s Kenn, Liking your little signature at the bottom very funny

jimeby

iTrader: (1)

This is getting to be a fun discussion... as my mother used to say, "it's the difference of opinion that makes a horserace."
Here's some answers to a few comments I saw:
Since we always skip gears during our braking into a corner, that technique has become our rhythm. If you bounce back and fourth between techniques, that is when you run the risk of loosing your rhythm.
Each time you change gears going into a corner, you upset the car slightly. If we only change gears one time, then the car is upset less and gives us a smoother corner entry. Plus it's less things to do so we have a tiny bit more concentration for getting thru the corner.
If we downshift half as many times, then there's half as many chances to screw up.
Our brakes are just fine on their own. Plus with extra downshifting, the engine breaking is not constant on entry, so this means the brake bias is constantly changing as we enter the corner, so the car goes loose, tight, loose, tight.
We wait until the very end of the braking to downshift so over reving is not an issue with us. And (he he) if we're downshifting half as many times, there's half as many chance to over rev so we're safer than most.
Well, no we haven't won every race although we win our share and a couple championships to boot. I think the best would be for us to all get together, we'll be happy to let you show us what you can do against us. Your next chance will be Thunderhill at the March double nationals. We'll be there clutch/double clutch/double declutch/trail brake/gear skipping our way into automotive history.