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Professional Motorsport Data Analysis: Steering Data & Balance

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Steering Data & Balance

12.28

00:00 - When we talk about analysing steering data, we're generally talking about using the steering angle input data.
00:06 This most commonly comes from a rotary potentiometer, connected by a belt driven from the steering column.
00:13 Alternatively it can also come from a linear potentiometer, attached to the steering rack.
00:19 Regardless of the source, it's telling us when, where and how much steering input the driver is using.
00:27 This can be one of the most useful sensors to have because it helps us understand what's happening with both the car and driver in a number of different parts of the track.
00:36 It can show us clear differences in driving style, driving lines, balance, stability, grip and more.
00:44 So let's take a look at some raw steering data to get familiar with it.
00:48 Using the speed trace as a reference, we can see how the steering angle is close to zero when the car is on the straights, along with the small corrections that the driver is making.
01:00 As the driver is slowing the car, we can see how aggressively they're turning into the corner.
01:05 The point of maximum steering is at the apex of the turn.
01:09 And we can see how the steering is gradually reduced as the car accelerates out of the turn.
01:14 Notice how the steering data follows our convention of positive values, being left hand turns.
01:21 Let's move on to looking at some specific handling traits and how we can identify them in the data.
01:26 One trap that's typical for amateur drivers is turning in too early.
01:30 if the turn in begins too soon, this naturally tends to make the later part of the corner sharper.
01:36 This is simply a natural response that happens subconsciously in a similar way to braking too early.
01:42 The impact of making the later part of the corner sharper is that the driver will have to slow more to make the turn which is obviously something we want to avoid.
01:52 Different driving lines are needed in different situations but in general, we don't want to make the track any tighter than it needs to be.
01:59 Comparing these two drivers, we can see that the orange driver begins the steering input earlier.
02:04 Later in the turn, this results in more steering input at the mid corner which is a common sign of understeer where the driver is trying to get more rotation out of the car by adding steering input.
02:17 We can also see in the speed trace that the apex speed is lower for the orange driver.
02:21 In this case it's not a case of genuine understeer it's just that the car needs to be turned sharper because of the early turn in.
02:30 Looking at the variance channel shows us the time/loss for the orange driver relative to white for this difference in technique.
02:37 Braking or entry stability is also something we can understand with the help of the steering trace.
02:42 It'll destroy a driver's confidence in a car and their ability to drive it close to the limit.
02:48 So it's something we want to get on top of really quickly.
02:51 Here's a car slowing for a relatively slow corner going from 5th to 2nd gear.
02:56 We can see that when the driver initially hits the brakes, the steering trace remains relatively calm.
03:03 However later in the stop, long before the turn in point, there are some significant corrections going on.
03:09 In this case, this is a sign of a braking stability problem.
03:13 The driver is making steering corrections if they can feel the rear end of the car starting to come around on them.
03:20 There are a number of potential causes for braking stability issues.
03:23 It could be a mechanical imbalance causing the rear to lose grip or brake bias being too far rearwards, down changes causing shocks to the rear tyres, aerodynamic issues caused by the centre of pressure moving too far forwards, rear tyre degradation or something else completely different.
03:43 Let's add the brake locking channels that we made earlier in the course to this plot.
03:48 Here we can see there's a significant amount of rear end locking going on which is a good recipe for entry instability.
03:55 Any rear lock with magnitudes as big as this is going to cause a lot of instability as the rear tyres aren't going to be able to provide much lateral support to the rear of the car while they're over saturated with longitudinal force.
04:08 The fact that the locking is so unsteady like this will make this effect even worse as any unsteady actions will tend to make any kind of instability worse.
04:18 Looking at the gear position trace, we can see that the locking looks like it's happening right around the time that the gear changes are taking place.
04:27 Which is telling us that the downshifts are likely the cause of the rear locking and therefore the stability issues.
04:33 Digging into it a little further, we can also see that the throttle blips are really inconsistent.
04:40 Each of these should ideally be about the same height and shape.
04:43 Looking at the modulation of the brake pressure while the downshifts are going on, we can see that this is quite poor.
04:49 Having unsteady brake pressure will only further exacerbate any locking or stability issues.
04:56 Using these channels together, we can see it's pretty clear we have a driver technique issue to address to tidy up and smooth out the downshifts.
05:04 Rather than it being caused by a mechanical or car setup issue.
05:08 When we get to the mid corner phase, looking at the amount of steering input can tell us a lot about the steady state balance of the car.
05:15 It's a natural response by the driver that their steering input automatically changes based on the balance they sense.
05:24 Broadly speaking, a car that has more oversteer balance requires the driver to use less steering input and the car with the more understeer balance will tend to have more steering input.
05:35 The question is, how much steering input is the right amount.
05:39 One way to answer this is by using overlays from a faster lap.
05:43 Here's an example of the same car with 2 different drivers.
05:48 At the apex, we can see that the driver of the orange car is both applying more steering input and holding that steering input for longer.
05:57 This is a typical understeer situation where the driver senses the car is not rotating enough and even though they understand adding more steering lock will not give them the response they're looking for, they do anyway which is a natural response.
06:11 Regardless, in this situation we can clearly see that the orange driver has more of an understeer balance than that of the white driver.
06:19 There are many potential reasons for this but one thing we can see in the speed trace in this case is that the orange driver is carrying more speed late into the corner.
06:30 In this situation it looks like for this particular slow corner anyway, a better approach may be to slow the car more on entry which will result in better rotation earlier in the corner as we'll be asking less of the front tyres on the entry and turn in phase.
06:47 Another way to look for understeer at and near the corner apex and whether too much steering input is being used, is through the lateral acceleration. We know that if we continue to get more lateral force out of the tyres, we'll get a higher lateral acceleration of the car to go with it.
07:03 By adding the lateral acceleration to this plot, we can start to get an idea of how the steering and lateral acceleration compare.
07:11 Looking at this corner, we can see a gradual input of steering as the corner goes on.
07:16 Looking at the lateral G force, it's obvious that even though the steering input is increasing, the lateral G is actually dropping off.
07:25 This indicates we've passed the peak slip angle of the front tyres as they're not producing extra force for the increased steering input.
07:32 Too much steering angle is being used here, if we then add a scatter plot of lateral G vs steering we see something that resembles the lateral tyre data we saw earlier in this section.
07:44 Putting these next to each other we can see a common trend in how the lateral acceleration is dropping off in this plot with additional steering and slip angle.
07:53 It's important to know that we're not comparing the same quantities here.
07:58 In the theoretical data, we're plotting lateral force vs slip angle and in the logged data, we're plotting lateral acceleration vs steering input.
08:07 With that said, it's useful to note that we get a similar shape to both and this is because the underlying reason for the behaviour is the same.
08:16 Using this plot gives us a different perspective to help us understand whether too much steering input is being used for a given chassis setup and section of track.
08:26 And by understanding its relationship to the theoretical behaviour of the tyre, we can make use of it.
08:33 The final phase to discuss is corner exit, in particular, we'll consider corner exit oversteer.
08:39 One of the most common times we'll experience exit oversteer, particularly in a rear wheel drive car is following an understeer that occurred earlier in the corner.
08:49 Throughout the corner, the driver will have been getting frustrated with the lack of rotation and the feeling that more steering input is not helping.
08:57 This will usually lead to a delay in being able to get back on the throttle while they wait for the car to rotate enough to drive out of the corner.
09:05 If the driver does start applying the throttle too early then in itself, this can make the understeer worse which leads to more aggressive throttle input as the driver tries to provoke the car to rotate.
09:18 At a certain point, the rear tyres will exceed their available grip and begin to break away.
09:24 We can see this happening in this section of data at corner exit.
09:28 As the rear tyres break away, the driver must use a lot of steering correction to help keep the car under control.
09:35 This whole understeering leading to snap oversteer scenario is quite common but regardless of the reason for the exit oversteer, this is how it will show up in the steering trace with a lot of rapid corrections, we'll start with the steering trace going in the opposite direction for the direction of the corner.
09:53 We can make use of some of the steering reporting channels that we previously created in the advanced math channels section.
09:59 Steering roughness and steering integral seen here alongside the raw data.
10:05 When we're looking for handling trends, and particularly how they evolve over a race stint, looking at lap after lap of raw data is often not particularly helpful or time efficient.
10:17 We want to use the reporting channels that summarise things and help point us to areas of the log data we should be focusing on.
10:24 Steering smoothness, while it can be a function of driver style and technique, also tells us something about how stable the car is.
10:33 Something that can become more obvious if we extend the smoothness channel even further to only calculate the smoothness on entry and exit separately.
10:43 In this case, we can see that as the stint continues, the smoothness reduces, indicating that the driver is using more correction as the stint goes on.
10:53 Selecting a lap from close to the start of the stint and one near the end, we can see where this difference is coming from.
11:00 It's obvious to see here that as the rear tyres degrade, the driver is doing many more steering corrections on corner exit which is giving us the difference in the smoothness reporting channel.
11:11 Now looking at the steering integral reporting channel which is giving us a metric for how much total steering input is being used over a lap, we can see that it's increasing as the stint continues.
11:23 A higher steering integral results from more total steering input over a lap.
11:28 Indicating that the balance is moving more towards understeer.
11:32 Looking at the raw steering data from laps at each end of the stint, we can see the cause of that in a number of corners with mid corner understeer, relative to earlier in the stint being quite clear.
11:44 In this case, this was due to front tyre overheating and degradation.
11:48 Lastly, while it's crucial to have an understanding of steering data, it's also important to recognise the value of driver feedback.
11:55 The driver feedback and what you see in the data need to be considered in parallel.
12:00 We need to be able to correlate the two.
12:03 Everything to do with cornering balance that we've seen in the data is relative.
12:08 Relative to another driver, setup, a tyre set, whatever it might be.