Hello Everyone,

This is indeed a great discussion! I have followed all of the posts and I've been trying to think of track's/situations where a trailing-brake maneuver is desirable. I've driven on the three Northern CA tracks extensively and have some familiarity with Buttonwillow, having driven it a few times.

First a bit of definition may be in order here, all of the inputs to the conversation thus far have talked around trail-braking, so I will define it; perhaps the definition will add more clarity.

Trailing braking is "trailing off" or decreasing the braking input while at the same time turning into a turn -- meaning the driver is turning the wheel while she is decreasing her pedal pressure on the brake pedal. The intent is to induce weight transfer (as previously stated by others) while increasing the slip angle of the front wheels -- a wheel traveling straight has a zero degree of slip relative to direction of travel, all other things held equal. (Candidly the degree of toe-in/toe-out generates its own slip angles, for the sake of discussion and clarity of point, we shall assume zero-toe. Even considering the disposition of toe the slip angle definition is relevant.)

Slip Angle, in this conversation, is the degree of lateral moment exhibited on a tire relative to its direction of travel. The angle is the difference between the two.

By introducing steering input (the driver turning the steering wheel) a degree of slip angle is created at the front wheels; couple this with the weight transfer the tendency will be for the rear of the vehicle (any vehicle) be become unladen, due to the weight transfer and to begin to exhibit yaw characteristics -- due to the slip angle introduction.

Yaw is a term best used to describe the rotational characteristics of a vehicle in motion, you may have heard the term "yaw angle".

The weight bias in a rear engined car will make the yaw characteristics more pronounced.

Trail braking is a very, very advanced maneuver as the driver is intentionally introducing instability with the intent to get the car to rotate (yaw). I have students (novices and beginners) ask me about the technique quite a bit. The issue is that if a driver does not have the appropriate feel for the amplitude of the car's rotation, the car can over-rotate and spin.

It was mentioned that it is best to get the car slowed down early (while traveling straight) and then turn into the turn, etc. A practice recommended by racers and instructors, this one included.

This is a much more stable way to present a car into a turn. Essentially once the car is turned-in -- meaning it has made the transition from traveling straight to turning, the throttle can be applied and the car will exhibit a stable progress through the turn.

Too abrupt a throttle can result in throttle induced oversteer. This occurs when a too-heavy throttle application introduces wheel slippage (where the wheel {tire} has broken traction with the road surface). Couple this with the yaw characteristics that any car exhibits while turning and you can see how a spin can occur in this scenario.

The spin; is much less terrifying and more easy to correct when it is throttle induced. Brake induced spins happen at higher speeds and with much less warning; once they being they tend to end badly.

I hope this is helpful.

Cheers!

 

T. Marc,

Have you experienced this instability when trailbraking? I have always thought trailbraking provide added stability if you are letting of the brake gradually. Only if you try turning before hitting the brakes will the car be unstable IMO. If you start off straight line braking you should not feel any instability under trailbraking. I guess it could be dependant on the type of car as well, but I havent experienced that in my Turbo.

And I have been under the assumption that trialbraking is for very long or off camber turns where the car tends to push, otherwise why be braking when you could have been carrying speed or on the gas?

Now high speed turns and trailbraking are different, if you are 50+ mph all the way through the turn, then you may want to reconsider the safety aspect of it, but normal turns should not make the car unstable.

 

Hello Heavy-Chevy,

When I wrote instability, my intent was to show that the maneuver itself created an instability in terms of the physical forces exerted on the car; not necessarily suggesting that the car will become too unstable to drive.

In other words, if you stood on your tip-toes and leaned forward at the waist, you would become unstable; you would not necessarily fall over. I was attempting to convey the same sentiment.

Braking and turning at the same time can be pretty advanced; the original poster mentioned that he did not have much experience with Porsches at speed.

Turn 2 at Thunderhill; Turn 6 at Infineon are two turns where if one really wanted one could trail off the brakes while turning for the purposes of getting the car to rotate into the turn. They are both of the gradual and sweeping variety it is indeed more stable and quicker to be in throttle application as opposed to brake modulation in those instances.

Quicker, because one is on the throttle for a longer period of time, more stable because throttle application tends to be a stabilizing factor other things held equal; especially in Porsches where we have the great benefit of weight behind the rear axle.

In the case of an off camber turn like Turn 3 at Thunderhill, the track is already falling away from the direction of the turn and thus the car will rotate into the turn.

To be clear, there are subtleties and nuances and personal preferences/experience levels, etc. Generally speaking trailing braking and other such techniques are best left to the advanced track driver, familiar with their subtleties and complexities.

Generally speaking the vehicle rate speed as expressed in terms of MPH/KMH is not as key a factor of determining speeds into and out of corners. Fast corners are driven a certain way and slow corners a certain way.

 

I get leery when I start to hear too much theory.

 

I forgot...you need to wear a stylish suit as well...










And I know exactly what you (T. Mark) mean by the instability and feel the same as you about it.

Heavy, just think of it as while your car is rotating...does it FEEL stable? No, because its shifting weight/rotating. But unstable and "unpredictable" are very different. Again, I think this is just a difference in the definition of the key-words in of this subject. You are just comfortable with that instability...as many of us are!

 

Oh ya, got to have the stylish suit! (Sharing a beer after a day of private driving instruction with Dominik Farnbacher)

 

BLUE LIGHTNING!


BLACK THUNDER!



UNITE!
























Ok, sign that I need to put down the sugar bowl and slowly walk away...walk away....

 

nice pictures Sechsgang, looks like fun. also, i forgot to mention that Hamilton has me on speed dial :-)

 

too cool...

We need a huge national 6speed track event so badly...

 

i agree! you are in philly, I went to Lehigh, small world. what track is that in your avatar? mine is infineon, turn 2.

 

Poser

 

thats at Pocono, but I got some shots from summit pt during my clubrace that Ill get on here some time...Im never the one who asks for pics, so most are from a guy that works at Pocono (even though I have been at VIR, Pocono, SUmmit Main, Jefferson, WGI, LRP and Laguna Seca).


Ill tell you what, Pocono running the reverse IMSA course...mmmmmm...185 feels so good!

 

Thanks for your support...***...


btw, Im definitely doing RAt. Clubrace...see you there if not at VIR first.

 

ahh really??

sweet...

We're gonna blow your a$$ away!!!!!!!!

 

i know what you mean about a course in reverse; ran Thunderhill in reverse this year, had a blast -- by the way I don't think my little car is as fast as yours if you are hitting 185 :-)