As multiple world champ Jackie Stewart once noted: “The key thing is not so much when you get ON the brake pedal, but when you get off of it.”
Threshold Braking & Beyond
by Jerry Austin, Ross Bentley, Satch Carlson, Peter Krause, Burt Levy, Chris Sneed and Ingrid Steffensen
One of the most gratifying experiences in publishing this niche magazine for track day enthusiasts has been the opportunity to meet with and talk to the most accomplished drivers who happen to also be very generous in sharing with us their expertise. Each of these experts enthusiastically jumped onboard and agreed to contribute to our driving technique series. In fact, when we asked Satch Carlson to write about threshold braking, he said “Oh, HELL yes... I'll be happy to maunder on about the joys of sheer terror, segueing into total blind panic!” We know you are hungry for technique related articles. So periodically, we will be surveying our panel of subject matter experts and combine their input into one single article covering a specific driving technique from multiple perspectives. We are very excited to share with you our assembled experts for this first go-around: Jerry Austin of Austin Motorsports, specializing in data analysis and data logging equipment; Ross Bentley of Speed Secrets and driving coach; Satch Carlson, Editor, Roundel Magazine; Peter Krause of Peter Krause and Associates and driving coach; Burt Levy, vintage racer, coach, columnist and novelist of many books such as his acclaimed The Last Open Road; Chris Sneed, owner of Sneed’s Speed Shop, instructor for PCA, BMW CCA and NASA, and professional racer in the Pirelli World Challenge series; and Ingrid Steffensen, BMW CCA instructor, professor, author and contributor to Bentley's Speed Secrets.
When I attended the Skip Barber Racing School, one of the exercises focused on threshold braking. We practiced the technique over and over in the old turn nine at what used to be Moroso Motorsports Park, now Palm Beach International Raceway. We used an access road to quickly circulate around and around back to turn nine to practice threshold braking. In this way, we could practice in front of the instructors and repeat the technique about once every minute. The Skip Barber School method involved our locking the brakes to get the feel for how much pressure it took to reach lock-up. Next, we were instructed to reach lock-up and lift our toes to release the slightest amount of pressure from the brake pedal. This small amount of pedal pressure adjustment was enough to unlock the brakes which became the reference level for reaching the point just before brake lock-up. Once mastering the sensitivity of this feel, we then practiced braking just up to the point of lock-up. In the process, turn nine at PBIR became my favorite turn, which proved to me that, if given the chance to practice an exercise where you could approach the same turn over and over without having to circulate all the way around a track, you could increase your proficiency at each turn one at a time. Hence, the advice to focus on one turn at a time during a track day.
Let’s turn now to our subject matter experts for their advice on threshold braking.
Jerry Austin of Austin Motorsports. LLC.
Threshold Braking from a Data Analysis Standpoint
In a hard braking zone I look at these items:
- How quickly does the driver go from full throttle to start braking (0.2 sec optimal)
- How quickly do they go from start of braking to full brake (0.2 sec optimal)
- Brake pressure profile has one peak, at the beginning of the braking
Ross Bentley of Speed Secrets
Thoughts on Threshold Braking
Threshold braking, where you're braking with the tires right on the threshold between continuing to rotate and locking up and skidding, is a technique that all performance drivers need to learn. Having said that, with most cars at track day events these days being equipped with ABS, it's becoming a bit of a lost art. But still, even with ABS, one can threshold brake - the difference is that your goal is to keep the tires on that threshold between continuing to rotate without relying on the ABS, and not braking hard enough.
The initial application of the brakes is something that's talked about a lot (the release of the brakes much less so - but that's a topic for another day). Every car requires a different amount of pressure, and more importantly, a different rate of how quickly you ramp up to that maximum pressure. Most performance drivers have been told to squeeze the brakes, and that's good basic advice. However, many drivers don't ramp up to the maximum pressure - where the threshold is - quickly enough because they're trying to squeeze too gradually.
As a general rule, older cars and those with softer suspension require a more gentle initial application - more of a gradual squeeze. Cars with ABS, bigger brakes, and less suspension movement reward a harder, quicker initial application of the brakes. The only way to know what works best for your car is to experiment with it. Try a harder, quicker initial application, and see if you're able to slow your car more quickly without it upsetting the balance too much. Keep testing that limit until you've gone a little too far and then ease up just a little.
Should you rely on the ABS entering every corner? Not unless you're driving a car that's designed for that level of braking - we're talking production-based, but purpose-built race cars here (Porsche 997, for example). A better approach with an ABS-equipped car is to only activate the ABS when you've gone beyond the limit. In other words, stay at, or just before, the threshold.
Having said all that, too many drivers think that they need to threshold brake for every corner, every lap, to be fast. There are many corners on many tracks where braking at less than threshold will result in you being faster. Think about weight transfer - when you're threshold braking, you're standing the car on its nose! That unbalances the car, and if you enter the corner with too much weight on the nose of the car, you'll have lessened the amount of overall traction you have. Plus, threshold braking may have over-slowed the car, so try a lighter brake entering corners and see if that enables you to carry more entry speed, rolling that through the turn, and still getting back to power good and early. Of course, it also puts much less wear and tear on your car. Instead of being overly focused on threshold braking, focus on how hard and quickly your initial application is, and how you release the brakes. That's what separates the fast drivers from all the rest.
In fact, threshold braking is way over-rated!
Satch Carlson, Editor, Roundel Magazine
I used to think that threshold braking refers to your ability to stop before your car actually crashes through the front door of a saloon, but nooooo—it’s actually a technique used to obtain maximum stopping power. The threshold we’re talking about here is the last instant of pressure before the wheels lock up. It’s a technique more useful in racing than on the street, because racers want to apply brakes as late as they can, as forcefully as possible—without locking up the wheels and sliding off the track. Finding that point requires practice.
Today, most drivers cannot even practice threshold braking without encountering the intrusive nannies of ABS. But at least those nannies let us know that we’re stepping slightly over the threshold! It’s actually a useful exercise to find out just how much force you need before the ABS kicks in.
Do not confuse threshold braking with trail braking, although many track drivers employ both techniques. Braking is generally best done in a straight line, especially heavy braking; if you brake hard on your way to a corner—perhaps threshold braking—and then begin your turn as you “trail off” the brakes, you are still loading the front wheels of the car, which helps the front tires steer into the corner. The goal is to make the transition from braking to acceleration so smooth that it’s hard to tell when you finally moved from the brake pedal to the gas pedal.
Or you could just lock up all four wheels, turn the steering wheel as you slide straight ahead, and then get off the brakes and stomp on the gas pedal, hoping the physics catch up before you hit the trees. This lurching caveman style is a terrific test of tire technology, and you may even get away with it once in a while. It works best on gravel. Ask me how I know.
Peter Krause of Peter Krause and Associates
Threshold braking is a basic, fundamental skill, that if practiced, mastered and made a primary part of a driver's repertoire, can make a big difference in covering a lap's distance in less time. Utilizing the maximum deceleration capability of the car, tires and driver, the maximum measure of braking is a relatively quick, high, constant or slightly dropping (but in a consistent way) longitudinal g reading. Basically, a benchmark for establishing the forward limits of the "friction circle," used in order to find out where the driver has opportunities for improvement.
So many drivers brake to what they THINK is the maximum capability of the car/tire, when in fact they are braking to the capacity of that THOUGHT, not to the ACTUAL capability of that car/tire.
The idea is to squeeze on the brake quickly and efficiently. When the pitch forward is largely done with and the weight is on the front tires (in a straight line), push down on the brake pedal HARDER, until you hear a small amount of tire squalling, chirping or other auditory signal that the tire is traveling slightly SLOWER than the speed of the car. Think of the shear of the rubber against the track surface generating the optimal slip angle of the tire in a fore-aft direction. Just like you try to do in cornering. The basic desired measure is the tire, retarded by the brakes, rolling slower than the rate of travel by between 4-7%.
The best way to hone the technique is to, without anyone behind you, pick a point earlier than you think you are from corner entry. Accelerate fully up to that point, squeeze on the brake pedal quickly and decisively, allow the car's nose to dive, then PUSH harder until the car feels slightly unstable.
Basically, you are trying to slow in the shortest distance possible from vMax (maximum velocity, Ed.) approaching the corner down to the desired corner entry speed. You WILL slow quicker than you plan, if done right. Then, take half the distance between the point where you end up at the desired speed and the geographic point at which you want to turn in and HALVE that distance. Take that off the front. Repeat. This is an incremental, safe way to find the proper initial brake point working back from the end. Called "The Procedure" by Skip Barber Racing School veterans, it works!
The point of the exercise is to build experience decelerating at a constant, maximal rate, altering the distance and therefore, the time you actuate the brakes to get rid of the required speed you need to negotiate the corner.
By taking one of the largest variables (sub optimal and variable rates of deceleration) out of the equation, consistency, lap times and predictability all improve, as does safety.
As seen by BS Levy
The phrase “Threshold Braking” gets bandied about on track days, in racing paddocks and around end-of-day beer rounds like it’s some kind of self-help pathway to stunning lap times. But I think over-concentrating on any single, particular aspect of track driving tends to move our focus, feel and sensitivity away from the natural, continuous flow and rhythm that are essential to doing our very best. I’ve always maintained that good racetrack driving should be like fine music: the circuit is the piece you’re given to play and your car is the instrument you’re attempting to play it with. And, just as in music, the really important thing is the melody and interpretation, not the wild, sizzling high notes or how bloody fast you can make your fingers fly over a keyboard.
Some random thoughts:
“Threshold Braking” simply means bringing the tires just shy (and here we mean JUST shy) of lockup in order to achieve maximum braking efficiency and the shortest possible braking distances. Which of course means you can keep your foot in the Loud Pedal longer on the preceding straightaway and, in the end, that’s where reduced lap times often come from. So a lot of self-proclaimed Master Drivers pride themselves on going as deep as humanly possible (or occasionally a bit deeper?) into every corner.
Modern ABS systems make the above pretty damn simple, as you can just STOMP on the bloody brake pedal with no finesse or delicacy to speak of and the little unseen nano-gnomes in the brain box do all the hard work for you. As an old, unrepentant stick-and-rudder man, I find this absolutely abhorrent. Like one of those eerie, upscale-shopping-mall grand pianos that play everything from faultless Brahms to cocktail-lounge standards to barrelhouse boogie-woogie with nothing but thin air over the keyboard. It’s just not natural, you know? I well remember the early days of black-box ABS and traction control in the old Firehawk and Escort series (precursors of today’s superb Continental Tire and World Challenge championships) and how some of the top teams would simply pull the fuse for those circuits (or install a blown fuse if they thought the tech folks might come looking) because they thought they’d be faster that way. But those days are definitely over, and many (but not all) of the currently available systems are better than even the most educated and sensitive human foot. I guess that’s progress, all right. And I think it stinks. And that’s why I prefer to spend most of my track time with the marvelous old cars and crotchety old farts on the vintage scene these days, where we still have to heel-and-toe/double-clutch every downshift and a paddle is something you use in a damn canoe. Say, who moved my cheese….
While highly useful in banzai overtaking maneuvers, Threshold Braking is not always the fastest way ‘round. I think the WAY in which the brake pedal is applied is perhaps more important than exactly WHEN it is applied. And when and how it is released is maybe even more important. That “roll-off transition” as the bottom of your foot moves from brake to power is where all the sensitivity, delicacy and balance comes in, and the whole idea is to make it fluid and graceful and not upset the balance of the car. As multiple world champ Jackie Stewart once noted: “The key thing is not so much when you get ON to the brake pedal, but when you get off of it.” And Jackie was not only super-fast, but unflinchingly clinical in his approach.
You need to remember that every section of racetrack is a continuing, on-going process, and the important thing is to gently SQUEEZE the brake pedal up to its comfortable maximum for any given situation and to likewise release it gently while rolling back into the throttle (particularly when attempting to rotate the car into a corner with a little signature-edition Skippy School trail-braking) so as not to upset the tire contact patches or the dynamics of the chassis. This doesn’t mean that you don’t get your foot down hard on the brakes, but rather that you get yourself there by way of coaxing and caressing rather than banging and bullying.
Demon late-brakers have a congenital tendency to over-slow the car due to too much concentration on how bloody deep they can go. Which is also how they often find themselves muttering: “did you see how unbelievably deep I went in there?” as the wrecker is pulling the remains of a bent car out of a trackside barrier.
In the end, it’s all about flow. I always tell students that fast is slow and slow is fast. When everything seems to be rushing up at you like spooks on a carnival ghost-train ride, you feel like you must be going fast because everything is happening in such a mad, manic frenzy. Only the stopwatch inevitably says “no.” But when everything seems to be taking place in measured slow-motion, when your eyes are focused far ahead and nothing feels rushed or edgy and everything seems to be flowing together like a lilting Strauss waltz…hey, that’s lap-record time!
Chris Sneed of Sneed’s Speed Shop, Instructor and Pirelli World Challenge Racer
Apply brake pressure quickly and firmly until you feel the tires release as they lock. Back off brake pressure slightly to keep tires just before lock up. If your car has ABS do the same as no ABS but keep the pressure on to just before ABS starts to work.
Easy way to learn: drive down the road at 30mph, lock the brakes and then release them until the wheels roll again. Continue practice until you can threshold stop without locking tires. Then increase speed by 10mph until you are at 60mph. Above 60 mph only practice on a track. Make sure you drive to the same mark to start threshold braking practice each time. More advance practice – do it in the rain.
Ingrid Steffensen, instructor, professor, author, and contributor to Bentley's Speed Secrets
You're an experienced driver, you have your favorite tracks. You already know where the brake point is--so don't look at it. As with so many things in both life and at the track--lengthen your gaze. Look deep into the corner and set your sights on the point of release, not the point of application. I swear this nugget is magic!
How to get to the threshold? Remember the brake pedal is not a switch--it's not on and off, it's a continuum. Resist the temptation to stomp! I know you want to. So do I. That's because it's scary when you're looking at Armageddon in the form of a tire wall. But instead, think of massaging a really stiff muscle--apply pressure firmly, with intent, but not to the point where you're doing a Fred Flintstone and putting your foot through the floor.
(Editor's note) It's not a coincidence that we heard about the Skip Barber School and the application and release process so many times. A term I like is: “Braking Backwards.” It means that maximum pressure in the braking process should be applied at the beginning when you are carrying the most speed and have the most downforce acting on the car. Then the pressure is gradually modulated off as you finish braking and start turning. The key to track driving is doing so with touch and feel. So, no caveman and definitely no Fred Flintstone stuff. Thanks coaches!