Telemetry: speed

Telemetry devices are a great way to investigate and improve your driving. From free smartphone apps to dedicated systems costing $5,000, there are a bewildering number of choices. The high end systems offer many more sensors and at higher resolution, but even the least expensive have some value. In fact, anything that graphs speed is really useful. To demonstrate this, let’s look at some speed graphs from some amateur racers (people I race with). To protect the innocent, I’ll call the drivers A, B, C, and D. The track is Willow Springs Raceway. For three of the drivers, it was their first time at Willow Springs.


The top 3 laps of Driver A are all within the same second, but they are highly inconsistent. The braking points are mostly in the same place, but how much the driver slows the car changes each lap. True, it was the driver’s first time at the track, but I suspect real culprit is that the driver wasn’t using reference points.


Driving Line

Driver B is much more consistent and a little faster. But look at the turn at the far right side of the graph (this is T9). Driver B only manages 95 mph at the end. Driver A is 5 mph faster. Why? Look at the shape of the speed graph. Driver A’s trace is V-shaped with a minimum speed of 70 mph. Driver B’s trace is canyon-shaped with a minimum of about 78 mph. But the minimum happens later in the corner. Driver A is on a late apex line while driver B is on an early apex. Look at the post for last week to see the theoretical difference.



Driver C is also driving inconsistently (again, first time at this track). But he’s a couple seconds faster than the other two drivers. Why? Simply because he hits nearly 110 mph as a top speed. Drivers A and B are slowing down in the fastest part of the track. Why? Probably because that part of the track is a little scary.



Driver D is ~5-7 seconds faster than the other drivers. His minimum corner speed is much higher than the others, but unlike Driver B, it does not trash his exit speed. A key feature of his speed trace is that the high speed corners (first and last dips in the graph) have U-shaped bottoms rather than V-shaped. This shows the driver blending cornering with deceleration and acceleration. Driver D is using a different cornering technique than the other drivers. Without steering, brake pressure, and throttle position, it’s hard to say exactly what that technique is.



Here’s how they all look in comparison. Green = A, Blue = B, Orange = C, Red = D.


2 thoughts on “Telemetry: speed

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