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Data Analysis Fundamentals: Lateral and Longitudinal G Force

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Lateral and Longitudinal G Force


00:00 - While it's possible to do a lot with the sensors we've discussed already, I'd also consider lateral and longitudinal G force to be on the essential list.
00:11 These sensors let us know how hard the car is cornering, braking or accelerating and give us a lot of information about the performance of the car and how well the driver is utilising the available grip.
00:24 In particular we can use these sensors in order to generate a plot of lateral G force versus longitudinal G force which generates a graph called the traction circle or a GG diagram.
00:37 We're going to dive into this topic in more detail a little further into the course but in a nutshell, this allows us to analyse the available grip from the car as well as how well the driver is able to utilise the grip as he or she transitions from braking to cornering and finally accelerating.
00:56 Here we can see the traction circle plot for a series of laps around our local racetrack.
01:02 Values below the horizontal zero axis indicate braking while those above indicate acceleration.
01:08 Likewise, to the left of the vertical zero axis indicates left hand corners and vice versa.
01:15 This plot shows us at a glance the maximum lateral and longitudinal G force that the car and driver are generating.
01:23 But just as importantly we can analyse how the driver transitions from braking to cornering and then from cornering to accelration.
01:31 By analysing how well the driver can ride the rim of a traction circle, we can learn how well the driver is able to exploit the available grip.
01:41 For the best accuracy, a standalone G force sensor is the best option.
01:47 This should be mounted as close as possible to the centre of gravity of the car.
01:51 Of course in most instances we're not going to know exactly where the car's centre of gravity is so we need to revert to what's practical, a location somewhere on the transmission tunnel near to the centre of the vehicle's wheel base is probably the most common compromise here and a pretty good guess.
02:09 To make our lives easier, many datalogging systems include built in three axis G sensors.
02:15 These also add vertical G force although for our analysis requirements, this third axis isn't really essential.
02:23 If you're using a dashlogger or a windscreen mounted logger with a built in G sensor, then the reading from the data will tend to be a little inaccurate due to the fact that the G sensor will be mounted well above the centre of gravity of the car and it's prone to errors created due to body roll while cornering.
02:40 In this instance, while the absolute numbers being generated from the G sensor might not be strictly accurate, the data is still useful in relative terms for comparing different drivers and potentially different setup changes.
02:53 Regardless of where the G sensor is mounted, it's important to make sure that it's zeroed before use which takes into account the mounting angle of the sensor or logging unit.