Braking Techniques


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These are old articles for previous models of iRacing cars that may have changes significantly. This was all designed for a TNT Racing app in 2015, but is now free to the public as a general guide. Some links may be broken and can no longer be updated.

 

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Braking Techniques 
The brakes in any race car are biased toward the front as weight transfer forward occurs every time you step on the brakes. The brakes on the front are usually bigger (physically more capable and larger with better cooling options) to cope with the tremendous loads put on them. In iRacing, there is currently no model for brake wear, so that discussion is removed and will be re-instated upon inclusion into the service. What racers should focus on is the shortest stopping distance coupled with proper apex timing and the working the car toward the apex, modulating weight transfer to stay on the absolute edge of available grip. When discussing maximum braking effort and minimum distance, the idea is to gain the entire grip available out of both the front and rear tires. When you brake too much, the tires at the front or the rear lock up. If the rear locks up, the rear of the car becomes unstable at times, resulting in oversteer and possibly an out-of control situation. Front lockups generally result in an inability to turn the car, longer braking distances, and missing the entry point. Optimal braking occurs just prior to wheel lockup. 
At this point, the wheels are rotating slightly slower than a one-to-one relationship of the distance traveled as the car slows. This can be found in telemetry when looking for lockups and partial lockups (Figure 1). 

Figure 1. Wheel Deceleration
When you find wheel-lock in telemetry (or in the car), try to recognize the instantaneous braking percentage to use as a guide for brake application the next time you brake at that corner (Figure 2). 

Figure 2. Wheel Lockup

It’s acceptable to have partial lockups. This means you are trying to get that perfect wheelspeed, but are slightly over, though not fully locking up the tire. Typically, the inside tire will lock up first if you have any cornering weight applied (as in trail-braking). The reason for this is the lack of weight on the inside tire as the outside tire bears the majority of the load. The lack of weight on the inside tire results in less pressure on the brakes to lock the tire as it is not pressed down on the surface like the outside tire. Partial lockups may occur over bumps which at times may be unavoidable when achieving optimal braking. Keeping the tire in contact with the ground is part of setting up the car, which is discussed in the dampers section, though it is applicable here as well. When the inside tire is unloaded during cornering, there are techniques that can be used to increase the weight on that specific tire so you can avoid lockups and continue to slow down with stability. An Anti-Roll Bar (ARB) affects how much body roll the car has. If you have a stiff ARB, the body will not roll as much which puts a little more pressure on the outside tire. If the ARB is too stiff, it might actually lift the inside tire off the ground which leads to full-lockup with minimal pressure. Lower ARB settings generally reduce inside tire lockup, but you may suffer some other consequences such as reduced aerodynamic capacity and spoiled airflow under and over the car. Dampers can place weight-delays on certain sections of the car, though this will be covered more extensively in another section.

The next important aspect is to item to find is the proper braking marker to use to begin braking. In real-world racing, a driver that has no experience at a particular circuit would brake early on the first attempt to try to find the correct spot to begin braking. Lap after lap, the driver would attempt to brake later as he or she found that later braking was optimal. IRacing has the added benefit of not having to pay for mistakes, so the ability to test and acquire the optimal braking zones happens earlier. Initial braking technique should be to max-perform the available tire grip all the way to any weight transfer required by turning the car. Using the “speed-delta,” in iRacing, you can find optimal times which roughly equates to optimal performance in a specific sector. It is usually best to use all the grip available to slow down, transition immediately from brake to throttle (using left-foot brake and right-foot throttle to quickly transition), and use throttle for as much of the corner as possible. Occasionally, trail-braking makes for optimal sector times.

All corners are different. Let us assume that we are entering turn 1 (T1) at Suzuka (SIR). This corner is unique in that it requires quick braking application and a slight trail-brake for the quickest sector time. The corner is also a “decreasing-radius” turn. The first half of the corner has a specific turn radius and the second half has a turn radius slightly that is slightly lower. In other words, the second half of the corner requires a slightly tighter turn based on geometry alone. This is the first thing that should be studied when dissecting cornering options. It is important to understand how a corner is designed and what the fastest way through the corner would be in a theoretical sense. As an example, let’s assume that after T1 at SIR there is a long straight (which, obviously, there isn’t). In this case, the proper line would be one that maximizes exit speed. If the following section was a slow-speed chicane, perhaps the best line would be one that minimizes time in the corners versus the previous example of generating exit speed.

Trail-Braking

Previous braking technique (straight-line) prior to turn-in works great, but in cases such as decreasing radius turns and various other types of corners trail-braking is optimal. Trail-braking simply means that the driver is using the brake during weight-transfer in corner entry to modulate grip levels and oversteer/understeer. As you begin braking, it remains imperative to reduce speed as quickly as possible as late as possible to arrive at corner entry with the correct speed to begin cornering. As you begin cornering, trail-braking technique is applied to continue to slow the car down while maintaining the perfect line to an apex. As you are able, transition from the high level of braking to no braking at the rate that allows maximum cornering G (if required) such that you can pick up throttle and use it to push to the exit point. To understand how this works best, weight transfer must be discussed in detail. Before we get there, let's discuss brakes from a setup standpoint.

Brake Bias

Brake bias (BB) is simply the pressure differential displayed as a percentage of front versus rear. 57% BB means that when you are under braking, 57% of the braking is done by the front brakes. 43% is accomplished by the rear. The effects of modulating BB can be quickly found with practice. As you decrease the number, you are asking the rear to work harder under braking which results in a loose sensation. If it's too low, you will lock up the rear tires and become unstable with the rear. If it's too high, you will find yourself stable until front wheel lockup which will send you straight, flowing with the camber of the road and the vector previously established at lockup. Best techniques for BB settings are to find comfort first. Once you are comfortable and not loose, bump the BB down a click to find a neutral setting that utilizes both front a rear brakes. What I look for when determining a BB setting is a place in telemetry where I am using the fronts and rears effectively (noting a deceleration of both ends of the car) and I am not finding the rear tires decelerating more than the fronts. I will look for trends throughout a few laps and determine if I have one end decelerating more than the other consistently. If so, I will move the BB setting to achieve similar deceleration rates throughout a lap. See Figure 3 for a snapshot of equal variance in front and rear deceleration rates. Sometimes a track will require a little more front or a little more rear. Adjust based on need. There is not one setting that is good for all tracks. Each track has its own nuances that should be explored.

Figure 3. Neutral BB Settings


Peak Brake Bias

Peak brake bias (PBB) is a setting that works in conjunction with "Begin Bias Ramping," (BBR) to achieve optimal braking. PBB is usually set higher than the BB setting and is used to slow the car down using the front brakes at a higher percentage. This is important when decelerating from high-speeds when there is an abundance of aerodynamic downforce which pushes the tires into the track at a higher level. When this is occurring, you should use more front BB as the front brakes are capable of more deceleration. The front brakes are physically bigger and can slow the car down more effectively than the rear brakes. PBB increases of 1 to 2% are generally good as a starting point.

Begin Bias Ramping

BBR is a linear transition starting point for the use of the PBB setting. If you are using a higher PBB than your BB setting, the BBR activates above the set percentage and decreases linearly toward your BB setting until achieving your BB setting at the BBR percentage of braking effort. That's a lot of words, so here's an example:

BB-55%
PBB=56%
BBR50%

At 100% braking, BB realized is 56%.
At 75% braking, BB realized is 55.5%
At 50% braking, BB realized is 55%.
At 50% braking and below, BB realized is 55%.

A nice way to set this up is to find areas in your telemetry where you are slowing down from high speed (anything 5th gear or less) and you transition to turn-in. Find the spot where you start to turn your wheel and note the percentage of braking at that point. check to see if there are other similar areas throughout the lap and find the percentage where you generally transition from straight-line braking to trail or no braking. This is your transition percentage. Note this percentage and set your PBB up 2% from your BB setting. Now set your BBR to the percentage you determined as your transition percentage. Now go test. If you find yourself locking up the front brakes, lower your PBB to about 1% and try again. If you are still locking up, increase the BBR such that you only use the extra forward BB at very high braking areas and you return to normal BB quickly.