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]

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]

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.

[FTS]

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

[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.

Originally Posted by TRAKCAR

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.

Originally Posted by FTS

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

[FTS]

Originally Posted by bman

All the cool people will be there

You too, darn it, I am missing stuff

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

[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.

[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.