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Data Analysis Fundamentals: Variance Channel

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Variance Channel

03.02

00:00 - There's a variety of ways of analysing your own performance in comparison to a reference lap.
00:05 You can look at the relative speed traces, which we already know will give us a good indication of where a gain is occurring, you can also look at the throttle use and see if there are areas where you should be getting on the throttle earlier or holding more throttle.
00:19 While these are important channels to analyse we're more likely to start with a slightly wider view of where the differences lie and we do this with a channel usually called something like variance, time delta or gain/loss, depending on your logging system.
00:32 This channel simply looks at the cumulative difference in lap time as you travel around the racetrack.
00:38 If you're comparing your own lap against a reference lap where you're 1 second slower, then you'll see the line for the variance moving around during the lap but ultimately it will end up at that same loss of 1 second.
00:51 Generally if you're starting out in this sort of position where there's a substantial difference in lap time, it can be hard to know where to focus your efforts, afterall chances are that you're simply slower and hence bleeding time everywhere.
01:04 Even in these cases, we can still start by analysing the low hanging fruit or in other words, look for the easy wins first.
01:12 What we want to do is to take note of the variance channel and look for the areas where it's changing most rapidly which will be obvious from the gradient of the line.
01:21 When the variance is steepest, this is where you're losing the most time.
01:26 When the variance is flat or only increasing slowly, you're doing much better relative to the reference lap time.
01:32 Initially, you might find that there are 3-4 obvious areas in the variance channel where you're losing the most speed.
01:39 And these will be the areas we want to focus on in more detail.
01:43 What we're going to be looking for is what's caused this variance.
01:47 We'll get into this in more detail but the usual culprits would include braking too early, not maintaining sufficient speed through a corner, or getting on the throttle too slowly on corner exit.
01:57 Of course driving lines can also play a big role in this too so it's important to be careful with your analysis.
02:04 One of the traps when using the variance channel is where you see the variance decrease, indicating that you're actually doing better than the reference lap, before increasing again sharply.
02:13 This can be misleading as it looks like you've made a potential improvement and it can be hard to understand how you've gone and then lost it all.
02:20 A good example of where we may see this is where you've braked too late into a corner.
02:25 Since you've braked later than the reference data, you'll be holding more speed for longer and this is why you see a gain.
02:31 The late braking however will compromise your turn in point because you'll be carrying too much speed to position the car properly.
02:38 This results in a compromise to your line through that corner, usually reducing the speed through the apex and affecting your ability to get back on the throttle at corner exit.