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Data Analysis Fundamentals: Traction Circle

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Traction Circle

03.20

00:00 - If we're logging lateral and longitudinal G force we can start to build a reasonably thorough picture of how hard the car can accelerate, brake and corner by analysing this data.
00:11 Trying to make sense of these individual channels on their own can be challenging.
00:16 So we can get a better understanding by combining the lateral and longitudinal G forces together on an XY scatter plot.
00:24 So this gives us what's usually referred to as a traction circle or the GG diagram.
00:30 The traction circle plot uses lateral G force on the X axis and longitudinal G force on the Y axis to represent the data in a logical manner.
00:40 As the car is driven around the racetrack, it's going to be able to develop a certain amount of lateral or longitudinal G force.
00:47 There's many factors that contribute to this but they're not really the focus of this particular module.
00:53 What we're going to consider here is how well the driver is using the available grip from the tyres as they drive around the racetrack.
01:00 Take for example a car that can generate negative 1.5 G under braking and 1.5 G of maximum lateral G force.
01:08 What we need to understand is that while the car can generate this level of G force in each direction, it's not possible to generate 1.5 G of braking force and 1.5 G of turning force simultaneously.
01:22 In order to begin generating cornering force, the braking force must first be reduced.
01:28 What this means is that on the track, the driver is constantly trying to balance the car on the edge of the traction circle, maximising the transition from braking to cornering and back to accleration as the car moves through each corner.
01:41 Of course, this is a lot easier in theory than it is in practice and the ability to use all of the available tyre grip is one of the skills that separates the best race drivers from those of us at the enthusiast level.
01:54 If we look at a typical traction circle plot, we're going to see thousands of dots representing each sample in the log file from the G sensor.
02:01 While this plot is referred to as a traction circle, in reality a racecar is going to be able to generate a lot more braking force than acceleration force.
02:12 So this plot actually looks more egg shaped.
02:15 The traction circle can quickly show how well the driver is using the full potential of the car and tyre.
02:22 If we analyse the maximum G force to the left and right, as well as the maximum braking force, we can approximate a circle that intersects these points.
02:31 What we then want to do is analyse how closely the samples follow this circle as the car transitions from braking to cornering and vice versa.
02:40 When you're analysing the data from a novice driver, you'll often see the traction tends to show almost a straight line between the points of maximum braking force and maximum cornering force, rather than a nice smooth curve.
02:54 This shows that the driver isn't exploiting the grip available as they transition from braking to cornering.
03:00 We'll see the same effect from the car as it transitions from cornering to acceleration.
03:05 However this tends to be a little less obvious since the maximum acceleration force is usually significantly lower than what can be generated under brakes.