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Professional Motorsport Data Analysis: Brake Bias

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Brake Bias

05.24

00:00 - The required braking force is never equal between the front and rear and for good reason.
00:06 The weight transfer from the rear axle to the front during braking means that we always need a higher proportion of braking force applied to the front axle, relative to the rear.
00:17 The ideal proportion of force supplied by the front axle is roughly equal to the sheer of the resulting vertical load on the front axle.
00:26 Generally when we talk about brake bias, we're talking about the hydraulic pressure bias supplied by the master cylinders to the callipers.
00:34 Due to the configuration of the braking system, where calliper bore sizes, brake disc diameters and friction characteristics are different, the hydraulic brake bias is unlikely to have the same value as the actual mechanical braking bias we want.
00:50 The mechanical bias, as discussed earlier in the brake temperature module, is also a function of the friction materials we're using and their operating temperature.
00:59 While we can calculate the ideal required and actual mechanical bias for our system, given enough information, it's more common to talk in terms of hydraulic bias as we can actually measure this directly which is what we'll refer to for the rest of this section.
01:16 Apart from initially setting the brake bias we want based on the specific components and application, there are a number of reasons that having an adjustable brake bias is helpful.
01:27 It's common for example to adjust the brake bias during a race stint to account for both fuel burn and tyre wear.
01:34 In the case of a fuel tank being close to the rear of the car, as the fuel burns off, we generally need less rearward bias now that less weight is on the rear axle.
01:44 The brake bias we need to account for when it comes to tyre degradation will depend on which end of the car is degrading the quickest.
01:51 We'd normally be reducing the brake bias away from the end of the car that has the highest degradation.
01:58 Brake bias is something that also needs to be considered when working with medium to high downforce applications.
02:04 In cars like these, as the vehicle speed changes, often so does the centre of pressure for the downforce.
02:11 In many cases, a different brake bias setting can help for different areas of the track, where the corner approach speeds are different.
02:18 Even with low downforce applications, varying the brake bias purely for mechanical reasons can be used to help mechanical balance by provoking more entry rotation through adding rear bias.
02:31 Or, alternatively, giving more entry stability by adding more front bias.
02:36 The session type also influences the brake bias we may want to target.
02:39 For example, during qualifying, we might target a slightly more rearward bias to help with entry rotation.
02:46 Whereas for the race, this may be too aggressive and would result in too much rear tyre wear over a full race stint.
02:53 The bias is also a useful tool to helping with any brake locking we might be struggling with.
02:58 Something we looked at closely in the previous module.
03:01 Here's an example of a driver who has locked an inside front wheel on one lap, then made a rearward bias adjustment for the following lap to help suppress that locking which is an effective use of their bias adjustment.
03:14 Taking a look at some brake bias data on a time/distance plot, using a channel that we put together earlier in the advanced math channel section of this course, the first thing we notice is how much the bias is changing during a stop in this car.
03:27 The amount the bias changes is a function of the dynamics, compliance and friction in the pedal box, master cylinders, brake lines and callipers.
03:37 Some variation will always be present but it's something we want to minimise because having inconsistent brake bias in different parts of corner entry can lead to imbalance issues that can take a while to hunt down if you're not paying attention to the brake bias.
03:51 A useful way to visualise the bias variation in the system is to plot the bias vs front brake pressure on an XY plot like we have here.
04:00 We can see that at low pressures, we have a lot wider bias variation than at high pressures.
04:08 We see a lower pressure when the brakes are first applied and as they're released, while the bulk of the stop generally consists of higher pressures.
04:16 The variation in bias at the lower end of the pressure spectrum is generally from friction and setup of the pedal box and master cylinders.
04:24 At higher pressures, this comes more from compliance in the brake lines, callipers and brake pads.
04:31 When we make physical component changes to improve our braking system, we'll often see them reflected in this plot.
04:37 A good way to look at our brake bias, particularly when it's adjustable is to calculate the average brake bias on a per lap basis and monitor how that changes throughout a run or race weekend.
04:50 By looking at the average value and resetting it so it's calculated individually per lap, we can create a report channel that can monitor the bias evolution.
05:00 Looking at this plotted over an entire run we can see how the driver is shifting the bias as the sting goes on.
05:07 In this case the driver is shifting the bias forward throughout the run as the rear tyres wear to help reduce rear locking.