Originally Posted by ProCoach

So, "trail-braking," AFAIK, was a term coined around 1974-75 with the crystallization of the curriculum at Skip Barber Racing School at Lime Rock Park. Skip has been featured in several videos and I've listened to some of his presentations about his formation of this concept. The best written tome on "trail-braking," as I and many others think of this fundamental skill (and how to execute it optimally), is in Carl Lopez's book "Going Faster: The Official Book of the Skip Barber Racing School." Quite detailed and very, very good.

Basically, he outlined how the phenomena of using a proactive strategy of control-input-relationship-to-directing-weight-transfer, past the traditional end of "straight-line/threshold braking," could reliably, safely in EXTREMELY efficiently aid in shortening the "rotation" moment and point the car in a heading more advantageous to progress to WOT (wide open throttle).

At the time, Jim Russell and later Bertil Roos were the contemporaries in this new business model of professional racing schools, and there was (and still is) a debate over what should happen in the period between EoB (End of Braking) and the apex...

Skip, mostly through study of other SCCA National Champions (he won Formula Ford in 1970 and 1971), then later, F1 colleagues, top-level F5000 and Can-Am drivers, described how the end of the slowing moment (in physics) and the release of the brake, WITH lateral forces well in play, could influence the car rotating on the outside front tire to aid the driver in changing direction.

This visible yaw was what he saw as common to all the great drivers he observed, particularly at slower corner entry well past turn-in but before the apex was clipped. This was DIFFERENT than the approach and technique some of the other schools were teaching, and he seized upon using this term "trail-braking" as one of the key differentiators in his curriculum and his school.

Most drivers who are not familiar with or even actually develop enough rotation to reduce steering input, for any period of time other than a premature correction, THINK they are trail-braking, hence the "watering down" of this important concept.

The entry to VIR Hog Pen through Turn 16A is NOT "trail-braking," because you are not TRYING to influence the car's yaw (or heading) through pivoting the car on ONE of the four contact patches, but people THINK they're "trail-braking" because they have the wheel turned AND they are applying brake pressure. That is NOT what Skip's concept was describing. Whay Skip was talking about was what MANY drivers DO successfully at the entry of Turn 4A...

Drivers who are continuing to brake PAST the initiation of steering input, but NOT enough to proactively CHANGE and CONCENTRATE the weight on the outside front tire, are not, in the classical term, "trail-braking." They call what they are doing "trail-braking" because they are "trailing the brake" INTO the corner, but the phenomena of using this to govern the weight transfer to effect the yaw, the rotation, is not there. Super easy to see on the data.

In order to eliminate confusion (which may have INCREASED it, inadvertantly), the SBRS curriculum renamed this concept and it's execution about twelve or fifteen years ago to a more descriptive "brake-turning" terminology. Which IS more "correct" and which is why that term is more descriptive and accurate, at least to me working with this concept nearly every day.

The goal of true "trail-braking" or "brake-turning" is to influence and LESSEN the amount of steering lock required to negotiate these slower corners. That's the real crux...

A dip between CombG (or gSum, same thing), between max braking and max cornering is indicative of NOT USING enough of the tire's demonstrated grip PRECISELY at the point of MOST desirable yaw, or rotation. Problem is, most drivers are nowhere close to equal or even near equal in those measures between Longitudinal axis and Lateral axis. LongG is usually half to two-thirds what the LatG measure usually is, and Buddy Fey has proven it needs to be not more than 10% spread.

It's a great question and one that data has helped illuminate in ways no human instructor can easily quantify. It also allows incremental increases in "asking" the tire and the car to do something that is hard to get used to! Great stuff.