hf1

You don't need to measure slip angle (in real time) in order to find and straddle the grip (friction) peak shown on the graph. In fact, that would be useless, as the friction curve (and peak) changes/shifts all the time depending on temps, tires, and track conditions. Butt-dyno works best.

DTMiller

I don't understand how you can determine where you are on the graph without objectively measuring it. Even if not in real time.

ProCoach

To measure something, you have to DO it first!

To measure slip angle with the accuracy of the graph pictured. Yes, you would need a powerful system with sensors and ideally, with multiple GPS antennas with a ground-level reference antenna, like this: https://www.vboxautomotive.co.uk/index.php/en/

But that would be only for validation, not as a tool "to drive to..."

I will say that the Apex DDC does encapsulate, package and present in real-time most of the ingredients required to GET there...

So yes, as a tool to validate what a driver is doing, that is a good one. The dozen or so I've sold so far, for those studying this information, have helped those folks significantly.

DTMiller

Right, but if I *think* I'm at the limit and an objective measure tells me my slip angle are 1* then what I think and what is real don't line up, so while I'm not measuring optimal slip angle I am measuring what is actually happening and without that measure it's harder (although not impossible) to change your mental belief about what you are doing out there and progress forward across the chart to the optimal ranges. And, conversely, to perhaps start reeling it in if you are somehow too far right on the graph.

ProCoach

Technically, that is true.

When I ride with people, if the car is tracking straight and true to the steered input angle, that is 0 degrees slip angle. No difference between the car's heading and the one selected by the driver...

When I take people for a ride, we often traverse some significant distance, through slower and quicker corners, with LESS steered input angle than how far the car is "pointed" or heading to the INSIDE of the corner.

The rider knows something is up, unsettling for the uninitiated (they think we're sliding, or borderline-out-of-control), but that is the sustained slip angle. No sawing, maybe minor corrections, but the trajectory of the car is different (wider) than the direction or heading the car is pointed towards...

The numbers are less important than the fact that they NEED to be generated and SUSTAINED.

Tire engineers often quote greater angles, specifically 7-12 degrees for DOT and R-Comps. That's quite a bit, when you're driving, more so when riding!

Listen to the podcast of Kenton Koch with Ross. It's very well explained.

hf1

The only way to find the graph peak is by overshooting it. The butt-dyno tells you when/if the grip falls off as you overshoot the peak. The only way to stay "at" the peak is by "straddling" it: constantly over/under-shooting it by as small amounts as possible. As the graph shows, the best "experts" straddle it the tightest. Most of the time their "corrections" (over/under-shoots) would be all but imperceptible to an outside observer.

ProCoach

I have to say that a) the scaling of that graph, on both axis, is NOT correct, and b) that MOST advanced drivers don't really "overshoot" the limit, they just interpret incorrectly that the RATE of slip angle increase is a loss of control or OVER the limit, when in fact it's just starting to get good...

Gary R.

This is the only slip angle I care about..

LuigiVampa

Glad to see we are back on topic!

Akunob

With all due respect, a car's limit is static. What you are describing (I.e., "unsticking the car") is what is actually known as reaching a tire's limit of traction/adhesion. Contrary to popular belief, when a tire reaches its traction limit, it doesn't simply break away resulting in the the car spinning out of control. A tire's traction limit is actually achieved within a range of slip angle. Beyond that range, the tire starts to lose grip progressively as the coefficient of friction drops. Some tires 'breakaway' progressively while others are more snappy, (I.e., for a car equipped with a given tire, its limit is STATIC, as the optimal slip angle is a known factor). What you are describing is a driver driving AT the tire's limit of adhesion/traction which is over a range of slip angle.

Driving a car AT IT'S LIMIT, requires the driver to attain and manage to the tire's slip angle to achieve the car's optimal cornering limit. A known fact is that many inexperienced driver's do not account for changes in track conditions (I.e., cool morning, vs hot afternoon) or tire condition (e.g., changes in tire pressure throughout the track day AND changes in tire wear over the course of a 2-3 day DE weekend). These factors AFFECT the tire's coefficient of friction and the size of the tire's contact patch which alters the tire's behavior, making it challenging for driver's to gauge a tire's limit consistently.

Remember the optimal slip angle HAS NOT CHANGED, the tire's characteristics HAS. The best drivers can make the adjustments, most of us (myself included) struggle with this. This starts to get very technical but as a driver I strive to understand these technical points which affect my car's behavior on the track as it dictates the adjustments that I make throughout my DE weekend.

A car's limit is FIXED for any given section of a track, based on what I described earlier, what changes are the track and tire conditions which necessitates changing driver inputs to consistently achieve that limit. Hope this helps.

ProCoach

Reading your more complete explanation, your idea of "managing the tire's slip angle" is what I call a variable limit. I think we're similar here, but I can assure you that the way a driver manages that limit is influenced a great deal more by the rate of change and the amplitude of all control inputs, even more than environmental conditions (other than rain... ).

Have you ever quantified these "changes in track conditions" or "tire condition"? It's quite illuminating and less than the variance in the range of grip (in any track or tire condition instance) over a range of slip angles. The "limit" is not a specific slip angle, more a range.

Good discussion, but I think your doggedness in stating that "a car's limit is FIXED for any given section of track" is not supported by your succinct explanation of breakaway characteristics or my many gigabytes of collected data from championship-winning professional drivers, as well as talented amateurs.

I'm looking forward to my :53 second laps at Lime Rock in a 150 hp car on bias-ply slicks, at slip angle ranges well beyond any fixed limit, next weekend!

dgrobs

I see hookers and blow in this thread's future (and maybe some French Landmarks)....

Akunob

ProCoach, apologies if I came off as dogged as it was not my intent. I blame the innate binary-bias in us folks whose profession (day job) has a quantitative element to it. Your characterization of 'variable limit' is accurate and a much simpler way to describe what I was trying to articulate. Thank you.

Re: Lime Rock, I run 1:02 on street tires in a 530HP car and I am switching to Pilot Sport Cup 2s in an attempt to crack a sub 1 minute lap (so I have much to learn). A run group with fewer than 35 cars would help. Enjoy your weekend at LRP :53 in ANY car is haulin'

Jack667

I think it's an interesting comment and observation, and pretty accurate. But I think there's also a feeling among many (not all) track day / DE drivers, that they drive under the limit on purpose. And I'm speaking of the amalgamation of their personal limit based on their experience, and that of the car / tires / etc.

I would further annotate the diagram with a blue star of the capability of a driver/car, and the orange star for how that person actually chooses to drive on a track day.

This could certainly translate into 'tenths', as in "I only drive at 8 or 9 tenths at a DE, when I'm in my street car that I need to drive home, and there's no trophy on the line."

There could be an arrow from right to left describing someone driving under their limit, and from left to right. I added a second oval to the right to describe a beginner exceeding the limit or overdriving the car...




From a personal example, I can provide an example of me at Road Atlanta, driving 3 consecutive laps at near PB times, all within 10/100's (ie a tenth of a sec, but accuracy to 100th). Because I drive almost solely at the orange star, that pretty much is my capability, because I refuse to further test the limits (mine/car) to move toward blue star or better. I refuse to invest that time and money, plus risk. So, yeah, I'm in your red oval, but I tell myself that I want to be there, and it's the very upper right of the oval, or maybe the orange star!

Cool discussion

ProCoach

And I agree wholeheartedly! Discretion is always the better part of valor, and the fact that people are thinking the way you describe is a GOOD thing. Did not mean to infer otherwise.