Clutch-in Braking For Better Performance?

[FTS]

During last two years, amongst the the NASA club racers and DE instructors, the technique of depressing the clutch in at the same time as you hit the brakes to disengage the engine from the drive shafts results in shorter braking distances has been discussed and advised. Even during our instructor training there was a short discussion, and frankly I dismissed it, did not even give it a second thought and forgot about it; I had other things to worry about, like getting my instructor license ;)

Last weekend at VIR, a GT2 driver reminded me of this and stated that he actually had good results. I tried it, and it does seem to yield noticeably shorter distances, especially under hard braking, for example T1 at VIR. It was too late in the weekend for me to collect data on either way, so I cannot prove it even to myself, but I intend to collect data during the Zone 2 event at VIR in March, and may be event at Summit Point the next weekend as well.

I haven't heard this in the Porsche circles yet, maybe I late into the game, but what do other think about this? Have you tried it, do you have comparative data, does it work?

[mooty]

what do you mean by clutch-in braking?

[Trackrat]

Makes sense off the top of my head- you are only braking the car, not car and all the moving parts of the drivetrain (additional inertial/rotating masses).

Hmmmmm

[FTS]

what do you mean by clutch-in braking?

As I understand the technicals behind the argument, which is an "if I understand it" :); when the gear is engaged, there is torque being transferred to driven wheels, which counter acts the braking force, at least that is the argument. So, as soon as you hit the brakes, you should also depress the clutch in to disengage the drive, so all you have is the braking force and it is supposed to be more efficient in dispersing the forward energy of the car. The other side of the coin is that when you don't transfer torque, the differential needs to be strong and aggressive to balance the car, preferably a 2-way LSD, not even a 1.5-way. But I am not sure of the technical merits, but at least I should be able to measure the results in couple of weeks ;)

[mooty]

if i have to down shift in that braking sequence, then as soon as i am on the brk, i floor the clutch, then heel toe to the gear i want.

if i am only braking without downshifting, which suggest not a very hard braking effort, i will not use the cltuch at all. i would think that if i used clutch for the short light braking effort, i would have to rematch rev with throttle blips as i let out the clutch. seems too much work.

[Gator Bite]

The momentum of the car is far greater than the rotational momentum of the drive train compoments and engine. In fact, the engine (with your foot off the throttle) will slow down a lot faster than you can slow the car with the brakes.

One variable that is changing is that this added friction is changing your brake bias by effectively adding breaking to the rear wheels. If your car can benefit from more front bias, clutching while braking will help. If it can benefit from more rear bias, it will hurt.

[Trackrat]

The momentum of the car is far greater than the rotational momentum of the drive train compoments and engine. In fact, the engine (with your foot off the throttle) will slow down a lot faster than you can slow the car with the brakes.

One variable that is changing is that this added friction is changing your brake bias by effectively adding breaking to the rear wheels. If your car can benefit from more front bias, clutching while braking will help. If it can benefit from more rear bias, it will hurt.

Yep, makes sense. Thanks for pointing out.

[FTS]

Is that theory? See, part of the discussion is exactly that: theory vs. factual data. I know I am too analytical sometimes, but that is the reason I want to capture data to prove to me first one way or another without the butt sensors' confusing me. Most of the time, our theories and body sensors say opposing things to us :)

[Larry Herman]

My take on it? Pure and utter bullshit. Just another wrong idea that some genius came up with. The last thing that you want to do is be playing around with the clutch as you approach a turn, especially coming down from a high speed.

In fact, since most cars seem to have greater front brake bias, reving to 6K and downshifting will provide significant engine braking to help with deceleration. Let the slow guys do clutch-in braking. http://forums.rennlist.com/rennforums/images/smilies/rolleyes.gif

[FTS]

LOLOL, that's exactly what I thought the first time I heard it ;)

[Gator Bite]

My take on it? Pure and utter bullshit. Just another wrong idea that some genius came up with. The last thing that you want to do is be playing around with the clutch as you approach a turn, especially coming down from a high speed.

In fact, since most cars seem to have greater front brake bias, reving to 6K and downshifting will provide significant engine braking to help with deceleration. Let the slow guys do clutch-in braking. http://forums.rennlist.com/rennforums/images/smilies/rolleyes.gif

I'm with you Larry. But be careful saying that in public. There are guys who have roasted me for suggesting that the engine can provide additional braking (at Planet 9).

I think that being smooth with the contol inputs will deliver far greater benefit (and speed) than the theoretical microscopic gain that you might be able to get by clutching before braking. This whole practice flies in the face of heel/toe downshifting and trail braking.

[Larry Herman]

I'm with you Larry. But be careful saying that in public. There are guys who have roasted me for suggesting that the engine can provide additional braking (at Planet 9).

I think that being smooth with the contol inputs will deliver far greater benefit (and speed) than the theoretical microscopic gain that you might be able to get by clutching before braking. This whole practice flies in the face of heel/toe downshifting and trail braking.You are spot on about being smooth with the controls and maintaining car balance & grip. I'll bet the guys who promote this are the "Kings of the late brakers" who slam on the brakes at the absolute last second and then just park it going into the corner.

When guys like Leh Keen, David Murry or Andy Lally start doing it, then I'll take notice.

[landjet]

Fatih, did you collect any data on this? I'd have to see the data to believe it. From all my Porsche and sports-car driving, I can't believe the "clutch in" technique works. Engine braking is a real phenomenon.

[FTS]

Nope, not yet, I have getting cosy with the new car, and trying this out was the last thing on my mind. Hopefully I will when I am at VIR with FSR in May.

Trakcar may try it with David Murry, and may be a short discussion with him while he is at VIR this month.

[TRAKCAR]

+1 bull. I already know what the coaches will say!

I try to go through all gears on the way down, unless I am taking it easy.
If taking it easy (lazy) I skip a gear sometimes, If I brake late and see that I might not make it I downshift a tad more aggressive to get max engine braking.

[FTS]

LOLOL, just as please when you are there, I am really curious. Do you know if Peter Kraus will be there? I am almost sure Mike of TPC will be there.

[bman]

The chief instructor for Nasa Mid Atlantic talks about clutch in braking a lot but to his defense he typically talks about it in terms of learning more about your car. I've never heard him say "this is how you should brake", typically it's his way of getting you to try different things to better understand your car's tendencies.


I try to go through all gears on the way down, unless I am taking it easy.
If taking it easy (lazy) I skip a gear sometimes

Funny, I am the opposite...all the gears when I am taking it easy and jumping gears when I am hot lapping.

Do you know if Peter Kraus will be there? I am almost sure Mike of TPC will be there.

All the cool people will be there :hello:

[TRAKCAR]

Funny, I am the opposite...all the gears when I am taking it easy and jumping gears when I am hot lapping.


Well, to be honest in the slower corners if I see at the end of braking zone I might be going fast I might skip gear 3 and hit 2 mashing pedal too, I was more thinking about high speed part of braking zone 6-5-4-3 where I know I braked a bit late, or the pedal does not feel as good as previous laps or sessions.

[FTS]

All the cool people will be there :hello:

You too, darn it, I am missing stuff :(

Well I'll bring photos from NY if you guys bring videos from VIR, deal? :pals:

[Dell]

I have tried both ways and I didn't see a huge significant difference in braking between the two. With that said, I would add that I prefer to "chase" the gears down through the box with (and here is the key) proper rev matching so the car is completely stable almost like an auto gearbox. The allows me to ALWAYS be in the proper gear with no need to find the proper gear should I need to alter, change, or bail in a situation. The time lost trying to get the right gear, guess the proper rev match at that speed, select the gear, and get back stable is the difference between escaping a potential bad situation and meeting mister armco.

[FTS]

... I would add that I prefer to "chase" the gears down through the box with (and here is the key) proper rev matching so the car is completely stable almost like an auto gearbox. The allows me to ALWAYS be in the proper gear with no need to find the proper gear should I need to alter, change, or bail in a situation.
Now, I hadn't thought about this benefit and it is good one. I don't raw the gears down, just jump from higher gear to the one I need to be in; however, I have to admit, there have been few times in which I missed a gear and the corner because my muscle memory wasn't ready for the gear I needed to be in vs. the gear I was scheduled to be in. Hmmm, something to think about.

Do you de-clutch as well with each gear selection going down the box?

[Dell]

Fatih, I found that it was easier to just jump down to the gear I needed but I also found that I had more errors so I started to change to the chasing the gears method. Some time back when I used to visit the racing/DE forum on Rennlist (when it was more civil) we had a thread about going through the gearbox versus skipping to the gear you want and there were definitely 2 schools of thought. I have never seen a pro racer skip to the gear he wants so I figured chasing the gears down the box was of some benefit since they do it. Once I got really good at my rev matching I felt more confidence to do it and the result was a car that felt more stable under braking. If by de-clutch with each you mean that I do the following for each gear, then yes: clutch, select next lower gear, rev match, release clutch. I go through that process for each as if the next gear down would potentially be my last gear selection needed.

Another reason that I didn't state why I chase down the gearbox is that with muscle memory, you will more often have errors grabbing the gear you are used to grabbing in a certain location on track and if the conditions have changed for that event or day or even lap you are more prone to the error of not grabbing the gear you need. Heck, conditions changing could mean you even had more grip and have a higher than normal entry speed that is controllable so 3rd would be better than 2nd.

If that sounded a little like one long run-on sentence it's b/c I haven't had a chance to down my coffee this morning and have a 1 and 3 year-old screaming for my attention. Ah, the joys of weekend mornings.......

[FTS]

Once I got really good at my rev matching I felt more confidence to do it and the result was a car that felt more stable under braking. If by de-clutch with each you mean that I do the following for each gear, then yes: clutch, select next lower gear, rev match, release clutch. I go through that process for each as if the next gear down would potentially be my last gear selection needed.

Another reason that I didn't state why I chase down the gearbox is that with muscle memory, you will more often have errors grabbing the gear you are used to grabbing in a certain location on track and if the conditions have changed for that event or day or even lap you are more prone to the error of not grabbing the gear you need. Heck, conditions changing could mean you even had more grip and have a higher than normal entry speed that is controllable so 3rd would be better than 2nd.

If that sounded a little like one long run-on sentence it's b/c I haven't had a chance to down my coffee this morning and have a 1 and 3 year-old screaming for my attention. Ah, the joys of weekend mornings.......

I guess it is something I need to practice and learn, thanks Dell.

I just woke up after watching the F1 race until 6 am, had a little coffee, and here I am :) What so abnormal about that :o

[Dell]

Abnormal is what us raceaholics suffering from Porscheritis call normal anyway :)