Racing 104 - Braking Technique

August 10, 2019

Racing 104 - Braking Technique

Key video points:

Threshold Braking - Braking at the limit of the tire's ability to grip the track surface.

Brush Braking - Braking using a softer input to slow the car, but not devoting the entirety of the tire's grip to deceleration.

Brake Turning - Brush braking where a slight turn is initiated during the braking application.

Trail Braking - Braking technique in which the initial deceleration is achieved through threshold braking, but soon after the driver feathers off of the brake pedal slowly and a balance between braking and cornering grip is achieved while the driver transitions from threshold braking to threshold cornering.

Braking is one of the most difficult skills to master both in the sim and real cars. And, it's one of the most important. There are several different types of brake pedal applications for different specific purposes. Investing time on developing better braking skills will have benefits not only in lower lap times, but also in better race results. Being able to brake as late as possible, or as little as possible before a corner allows you to maintain the highest possible speed for the greatest duration of time. Let's take a look at how to get this done.

Threshold braking refers to braking at the limit of the tire's ability to grip the track surface. This means that the driver can brake very late at the end of a long straight away. Corner 11 at Mazda's Raceway Laguna Seca is a classic example of a threshold braking corner. Braking at the threshold of lockup ensures that you're getting the most possible grip at the tires; once the tires are locked, the efficiency of the braking goes away, as the tire melts and abrades on the pavement. By keeping the tire rolling just slightly slower than the car is traveling, the maximum grip is developed at the contact patch.

Of course, not all situations require threshold braking. Many times an earlier, softer pedal, or brush brake, is all that is needed. For instance, Turn 6 at Laguna Seca for many cars is just such a brake application. many ovals require a similar technique, referred to as brake turning. This is where a slight turn is initiated during the braking application, and a balance between braking and cornering is maintained. If you're at 100% braking, there's no grip available for turning. If steering is added while at threshold, the tire will lock up unless some of the braking force is released. This leads to trail braking, where a slight rotation or pointing of the car upon release of the brake pedal at turn in, can be very useful. 

Mastering the various braking techniques is tricky enough in a real car; take away the physical sensations of movement,and the job becomes even harder to master in the sim. In a real car, the braking systems are all pressure-based. The harder you push, the more resistance. Only the best sim controls have this kind of setup. Most of the affordable pedals for the sim are position-based, meaning that you need to learn where in the pedal travel threshold braking occurs. Whether you use your left foot or right foot on the brake, there are some clues you can look for to see how close you are to threshold. In any of the open-wheel cars, you have the luxury of being able to see the tire rotation. The Skip Barber car is the easiest to start with, because of the tread pattern of the BF Goodrich G-Force Sport (Oh my god, I wonder if BF Goodrich sponsors iRacing? ... idiot). The next most obvious clue is the tire noise. here are subtle differences in the way the tires make noise as they get closer to the threshold. Each kind of tire will have a different sound, and headphones might be a better way than speakers to hear the differences. Steering feedback is another way to tell if threshold has been exceeded. Once the tire is locked, the steering has no effect; so if you have force feedback, you'll feel the steering get vague. And, if you turn the wheel, there will be little if any direction change. In any of the closed wheel cars, you'll have to rely on the sound and the steering to tell when you've exceeded the threshold. The Pontiac Solstice car has ABS, and therefore it's a car where you can just push the brake pedal as hard as you wish, and there will be no lockup. 

Key video points:

As we discussed in the Vehicle Dynamics video, you must think about the transfer of weight under a braking situation. When you apply the brake, the weight of the car transfers toward the front tires; this means the front tires have more grip than the rear tires. This transfer of weight is why braking systems have something called brake bias. Brake Bias is the difference in pedal pressure distributed to the front and rear wheels, and helps to compensate for this loading difference. It can be adjusted when setting up a car for a particular track. Too much front bias, and the front tires lock before the rear tires do; too much rear bias, and just the opposite will occur. If the brake bias is just right, your braking distance is minimized. Slight rear bias can help with rotation at turn in, because the rear tires will have a smaller contact patch and will be more susceptible to slip. The faster the car is traveling, the harder the pedal can be pushed before tire lockup. In most race cars, this is primarily because, at faster speeds, there is aerodynamic downforce that increases the tires grip. And as the car slows, that downforce, or the grip, lessens. This means that it's easier to get the brakes to lock the slower the car is going***. Therefore, the initial application is very important. You want to take off as much speed as early in the brake zone as possible, so that as you get closer to the turn-in point, you're able to modulate off the pressure. Modulation is also necessary if you lock the tire at any time during the braking application. Try to get the tire rolling as soon as possible with as little release of pedal pressure as you can manage.

Regardless of what kind of braking you're doing, start with a conservative, early brake point. There are few mistakes harder to fix than a brake point left too late. Establish what level of braking is available, and then work the brake point closer to the turn-in. If threshold braking, when you reach the point where it's difficult to make it to the apex, you know you've gone far enough. If braking and turning at the same time, experiment with subtle changes in brake levels to see the effect on how well the car turns in. For brush braking situations, try lighter pressure or shorter duration and observe the results. If you're trail braking, experiment with the rate at which you release the brake pedal, and observe the different rates of rotation. Typically, the faster you release the pedal, the more abrupt the rotation.

A good way to hone the braking skills we've discussed is to start with straight-line threshold braking. Pick the Skip Barber formula car and go to Lime Rock, and stop the car on the front straight before the start/finish line where there's an access road on the driver's left. Accelerate through the gears up to 3rd, and hold the speed at 6000rpm (revolutions per minute is not a speed, just so we're clear). Start braking at the 6-board and see how quickly you can bring the car to a stop. You should be able to stop it just before the 4-board. Notice the different tire noise between lockup and no lockup. Be sure to practice this many times. Instead of taking a whole lap to get back to the starting point, make a u-turn and drive back up. ONLY do this during a test session. For another practice session, select either the Skip Barber car or the Late Model, and go to a small oval track like Lanier. Here, work on brake turning skills, and experiment with different levels of brake and steering input. Next, try a great trail braking corner like Turn 2 at Mazda Raceway Laguna Seca. Again, experiment with different rates of pedal release while in the Skip Barber car, and observe the effects. If there is no rotation, you need more turn-in speed. Experiment with changing the brake bias for all of the situations we've mentioned and notice the effects. 

With a little practice and concentration on your braking techniques, you should see an improvement in your performance in braking zones and corners. Ultimately, this will result in smoother sailing on the track,and of course, faster lap times. 

Good stuff iRacing, good stuff. This is one of the areas where I personally have trouble; braking. It all seems so simple, but it's one of the most overlooked areas of improving one's performance on race day. The key to a good turn in point is your ability to consistently hit it right on the money, and at the same speed. If you have trouble braking in a consistent manner, your entire corner will suffer. As I showed under bold, there are FEW, if any, problems harder to resolve than braking too late for a corner, or not braking hard enough for a corner. The examples and practice problems in the videos really are good ways to observe and improve w you brake, and the various methods used to get the car whoa'ed down for a corner. Another great place to work on your braking is basically any roval; infield road courses such as Charlotte or the Daytona road course typically have a pretty difficult decreasing radius or high speed corner when entering the infield section from the oval. The infield complex at Charlotte Road is also a great place in general to work on your braking, and is very rewarding in the Skip Barber car. Brake as late as you can and all the way to apex in Turn 1. Brush braking through the horse shoe, trail braking into that tough uphill right turn, it's all very challenging. And, equally rewarding to see those times drop. See the article around the Racecraft Forum entitled Going Faster for a great write-up and data with this track and car combination. 

*** A note on aerodynamics. You may find that some cars that don't rely on aero may like a bit more consistent brake application. And, in cars like the Skip Barber which have a lot of weight towards the rear of the car, quick and hard application of the brake pedal may make it feel like the car wants to swap ends. Make sure to try out different braking techniques in a new platform and observe the effects. In cars such as the FW31 or Dallara, the great amounts of downforce generated will allow you to jump hard on the binders in high speed braking zones and shed speed quickly, but you will have to bleed off of the brake pressure upon initial input to avoid lockup as the force generated by the aero decreases. 

Regarding brake bias, it can be a really important factor to match to your driving ability. Typically, more advanced drivers will run more rearward-bias in their setup. This is because increasing rear bias improves your ability to rotate the car while brake turning or trail braking. In cars like the Skip Barber, again, a novice driver may opt to keep their brakes biased toward the front end more; this allows for more consistent and manageable behavior of the vehicle under braking, and too much braking while turning will simply provide a touch of understeer versus the car wanting to swap ends on you and head to the apex butt-first! We can use different braking techniques combined with properly adjusted brake bias to solve our handling problems as well. Let's take a look at our example.


Example:
Mid-Ohio Sports Car Course, full circuit
Turn 4 - "China Beach"

Problem - You notice that in your practice session (because you are an intelligent racer and spend many laps in practice becoming consistent with your chassis and track combination and learning how to deal with traffic at this particular event), most of your competition can get through turn four and into turns 5 and 6 of "Madness" quite a bit faster than you. Using the first Racer's Bible entry, you consider vehicle dynamics and immediately characterize your issue as understeer; In the second, you optimized your racing line to resolve this understeer. We'll solve it using braking technique this time.

The Braking Technique Solution -

You take what you know and understand to be understeer and consider what causes understeer from the racing line's point of view. After studying the video footage and checking your lap analysis tools on MoTec, you notice that you are locking your front tires often in the braking zone. You also notice during practice sessions that the quicker drivers tend to display quite a bit more slip angle through turn-in and at the apex point of China Beach. Looking a little further into the problem, it seems pretty clear that the gentlemen at the top of the time sheet are trail braking right up to the apex of China Beach. Using your knowledge of braking technique, you first make a conscious note to modulate your brake pressure to avoid lockup. This allows you to enter the corner more consistently, and you see a slight drop in time through this corner in your data. Great, but now what? You're still losing two tenths through just this corner. So, you try and trail brake into the corner. It seems to make a slight improvement your time, but you have not solved your understeer problem here. Since you are now using your brakes through the duration of turn-in, and you know that your front tires are definitely locking first, adjusting the brake bias rearward is your next step. This allows you to be more aggressive under threshold braking, as you've optimized the chassis to perform better under braking. You also can now use your ability to trail brake more effectively, as the rearward bias shifts the chassis balance under braking toward oversteer. You can now use brake pedal modulation to control whether the car understeers or oversteers slightly, and you're back on pace with the top 5 on the timing screen. In the words of Borat...

Great success!



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