I have never doubled clutched in my life.

I do heel and toe all the time on the track (every downshift) and quite often on the street. Heel & toe on the street is harder since the brake pedal is not pushed in as far thus the positioning of the gas is not ideal.

As for clutch wear... After 18 months and 20-30 races my stock clutch still had in the ink stamp markings on it. That is how little wear the clutch disc surface had.

 

Hmm...
Well I shifted my 944 from 4th gear at just over 100 mph (6000 rpm) into 3rd, never even rev matched. It when in just fine. I got lucky however I did not bend any valves from the over rev as I noticed it as was realsing the clutch. I know a few others who the same thing did bend valves. (sloppy shifter missing 5th when taking a 1.5G turn). Never any tranny damage.

Seriously you logic just does not hold.

 

Well I routinly enter a corner on one track I visit at abotu 130 mph in 5th. Then hard on the brakes. Sometime I downshift to 2nd gear straight from 5th. No double clutch.

The onyl issue I have is that due to long time it takes to slow to the 50 mph I need for 2nd gear I can get the timing wrong. So I have taken to putting the car in 3rd for short bit (never realeasing the clutch) then going to 2nd with a standard heel and toe. Seems to help my flow in the corner.

How many times have you thrashhold braked from 130 mph to take a high rpm 2nd gear corner?

 

YEP... I have been doing that to the same gearbox for 7 years.

 

Well I don't believe that is totally correct.

not rev matching on down shift requires the CLUTCH to make up for the differene between engine and tranny speed. The R&P does see some load, but that is filtered through the clutch. If you ease the clutch out then most of the goes into a slipping clutch. If you dump the clutch the there is a shock load that goes into the ring & pinion.


I think R&P failures are result of shock load either in accell or decel. Straight acceleration loading or even load from lifting off the gass at 6000 rpm and engine compression braking are not issues. These are the loads the gears are designed for. However shock loads from dumping the clutch in ether up or downshift is very hard use.

When driving on the track you NEVER shockload the rear end. At least never on purpose, but I can happen if you make mistake. The reason is not to save the r&p, but shock loading the rear end will cause a loss of grip in the rear tires. This is very likely to cause a spin.

 

I fully agree with M758. Double clutching is for vintage racing or getting around a blown syncro. I routinely drop into second from 4th under heavy braking at the track. With proper rev matching everything goes very smoothly.

 

That article that martin944 posted was good at explaining the mechanics of everything. I think CarbonRevo and M758 both have good points. On the street, I double-clutch when I downshift either of my cars because it does go into gear smoother and it is smoother for the passengers when it is done well. And once I got good at it, I can get into any gear (as long as it won't overspeed the engine), even if it is almost at redline, without making the car move at all. It's especially nice when I want to pass on the highway going from 5th to 3rd. But I don't ever do it autocrossing and wouldn't ever do it on a track because it's just a good way to loose concentration and loose time; I just slip into 2nd at the end of my braking zone (the syncros have time to spin up the input shaft as I brake) or as I trail brake and then rev-match a bit (sometimes heel-toeing or ball-toeing, but usually since I'm not that coordinated after I get off the brake, although obviously I can loose time doing this), get the clutch back out and go. But driving on the street, getting into 1st gear is so much easier if I double clutch. I read a book by a racing coach that discussed among other things downshifting while braking and the bad effects it can have on braking distances because of distracting the driver. This book did interest me in talking about race trannies with dogs instead of syncro-mesh, and that some race drivers shifted quickly on dog transmissions without the clutch at all. I'll try to get the title of the book for you guys. It's on motorbooks somewhere...
But at the very least it is fun to learn both. Never know when you might need to drive a truck or something without syncros; I've had to do it!

 

That is why we don't teach heel & toe downshifting in most DE's.

However it is an ESSENTIAL SKILL for driving fast on a race track. Not doing it leaves you very very slow.

 

[QUOTE=knfeparty] On the street, I double-clutch when I downshift either of my cars because it does go into gear smoother and it is smoother for the passengers when it is done well. QUOTE]

Why would double-clutching make downshifting smoother for the passengers? They can't feel the synchros working, so it seems to me that as long as you match the RPM's of the gear you're going into when you let out the clutch, that's what matters for smoothness.

 

Eh, good point kevin. I just got used to the rhythm of the double-clutching, I guess.

That book is "Drive to Win...The Essential Guide to Race Driving" by Carroll Smith. ISBN 0-9651600-0-9

from 1996. It's a really interesting read, but it is tailored towards drivers who want to become professionals and who would be doing formula or something like that.

 

Just making the point I have been doing this for a while. You are missing my point - I'm not arguing against DC - its a valid technique - mostly for upshifting - for transmissions with tired synchros. Its generally not used in performance driving.

I was referring the the fact that you might be overreving your motor when you release the clutch.

I would perform a fluid, perfect heel and toe downshift that would leave your head spinning with the ease and grace of how well it was performed. ;-)

On the brakes, depress clutch (still on brakes), perform shift while blipping throttle (still on brakes - ball of foot on brakes, side of foot controlling throttle), release clutch, release brakes, turn into corner.

I heel & toe downshift all the time on the track and just about all the time on the street. In fact, I would argue that if you cannot do it, perhaps you should be driving an automatic.

 

M758 has it right...

Yes - it takes some time to learn this properly and become fluid at it. The first performance driving school I took I was so worried about getting the heel and toe downshift right that I seldom got the corner approach or entry proper. A couple of years later I took a second school and I had my heel & toe technique down. I learned alot more during that school since I could concentrate on all the other aspects of driving and not be fixated on my downshifts.

Without heel and toe at the racetrack, one of two things will occur:

1) you will not be able to rev-match properly on downshifts before the corner and get the back end of the car all squirelly when you release the clutch and probably miss your turn in.
2) you will try and feed in the clutch during turn into the corner - you will screwup the balance and all of the guys who can heel and toe will eat you for lunch on corner exit since they are all ready to apply power.

 

Now you wonder why DC'ing is used? Trans...motor...same speed? Uh yea. Reving with the clutch in doesn't change the difference in motor to trans speed. That's pretty much been the point here. Rev matching only revs the motor, and your trans. still has to pick it's revs up when you start to let the clutch out. DC'ing revs the motor up, which in turn revs the trans up to the same speeds.

Enough said. Keep bickering if you wish.

 

You could always drift the corner

 

A good DC'er can do it almost flawless each time.