Lateral acceleration

Figure 1: This chart displays GPS speed (black) and GPS lateral acceleration (red) for the same rider, track and motorcycle as used in the longitudinal acceleration section.

Figure 1: This chart displays GPS speed (black) and GPS lateral acceleration (red) for the same rider, track and motorcycle as used in the longitudinal acceleration section.

Just as longitudinal acceleration is recorded by an accelerometer inside the data unit as well as through the GPS signal, lateral acceleration is likewise represented by two channels. In this case, however, the internal accelerometer cannot cope with a motorcycle application and is rendered useless. A full explanation is detailed in the next section. As mentioned previously, this is why GPS-based systems are so valuable, and any reference here to lateral acceleration will by necessity mean the GPS channel and data.

Figure 1 shows a GPS lateral acceleration graph with speed for the same track, motorcycle and rider as used in the longitudinal acceleration page. Positive lateral acceleration represents a right-hand turn, with negative lateral acceleration representing a left-hand turn. Note that the magnitude of maximum lateral acceleration is higher than that of longitudinal acceleration in this case; a standard motorcycle with street-oriented tires will typically reach a maximum lateral acceleration of approximately 1g; race tires and suspension will add more to that figure.

Figure 2: With longitudinal acceleration (blue) added, certain traits become evident.

Figure 2: With longitudinal acceleration (blue) added, certain traits become evident. However, it’s far easier to combine the two acceleration channels using an X-Y chart or math channel to gain the most benefit from acceleration data.

Obviously, lateral acceleration will be minimal on a straight section of track. With a lateral acceleration trace on its own, ensure that the rider reaches that maximum magnitude in each turn, even if only for a moment. In sweeping turns, lateral acceleration should be constant at the maximum value, as evidenced in this example in sector 2. In Figure 2, the longitudinal acceleration is added to the chart. The graph is getting somewhat cluttered at this point, but some traits emerge: Note that longitudinal and lateral acceleration are never at an extreme at the same time; maximum lateral acceleration only occurs when longitudinal acceleration is near zero, and high-magnitude values of longitudinal acceleration occur only when lateral acceleration is near zero. Where these two traces cross point to areas of trail braking or accelerating while the motorcycle is leaned over. Just as the two traces are never at an extreme together, there are only a few instances where they will both be zero. If both lateral and longitudinal acceleration are zero for an extended period of time, this is an indication that the rider is “coasting” when there should be some acceleration present.

While these characteristics can be seen viewing the two acceleration traces together, it’s far easier to look at certain details by combining the acceleration data using an X-Y plot or math channel, which are the subjects of the next several sections.

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