Clutch-in Braking For Better Performance?

FTS · #1 02-25-2011, 09:41 AM

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 · #2 02-25-2011, 09:03 PM

what do you mean by clutch-in braking?

Trackrat · #3 02-26-2011, 05:46 PM

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 · #4 02-26-2011, 11:02 PM

Quote:

Originally Posted by mooty

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 · #5 02-27-2011, 12:18 AM

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 · #6 02-27-2011, 09:26 AM

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 · #7 02-27-2011, 04:02 PM

Quote:

Originally Posted by 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.

Yep, makes sense. Thanks for pointing out.

FTS · #8 02-27-2011, 09:28 PM

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 · #9 03-10-2011, 09:09 PM

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.

FTS · #10 03-10-2011, 10:22 PM

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

Gator Bite · #11 03-11-2011, 09:19 AM

Quote:

Originally Posted by 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.

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 · #12 03-11-2011, 11:34 AM

Quote:

Originally Posted by Gator Bite

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 · #13 04-07-2011, 09:51 AM

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 · #14 04-07-2011, 01:37 PM

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 · #15 04-08-2011, 09:26 AM

+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.