 Most data acquisition systems...  Most data acquisition systems offer a dedicated rpm channel, and a sensor is not needed-the bike's tachometer signal at the ECU can be tapped into. Some bikes have weak tach signals, however, and it may be necessary to connect to a crank or camshaft sensor |
 This graph shows an rpm trace...  This graph shows an rpm trace (red) with ground speed (black) for a Yamaha R1 on Buttonwillow's west loop. The sawtooth shape indicates upshifts and downshifts. This data was recorded using our Racepak G2X GPS-based system. |
 Engine speed (red) and wheel...  Engine speed (red) and wheel speed (black) are shown here for a Suzuki GSX-R600 at California Speedway, with the blue line indicating gear position as calculated by a math channel. The data is from an AiM Sports system that is based on wheel speed-note that the rpm is almost always proportional to speed in this graph, and in the G2X graph there are variances due to changing tire circumference. |
 This section of data from...  This section of data from California Speedway shows two laps overlaid. In the first lap, with gray speed and light-red rpm traces, the rider hits the rev limiter on a straight before braking for a corner-note that both the speed and rpm traces are flat for a time. The next lap, with black speed and dark-red rpm traces, shows the rider upshifting then downshifting through the section. Segment times can determine which method is quicker in this particular case, or information from the entire lap can be used to make a gearing change. |
In last issue's Art & Science we discussed the basics of data acquisition and different ways to interpret speed data. Speed-whether recorded by a GPS-based system or a unit that measures wheel speed-is generally the base channel and offers plenty of information on its own. Adding more channels, however, allows a more in-depth analysis of the motorcycle's and rider's behavior on the track. That higher level of analysis can in turn result in quicker development and improved overall performance from both the bike and rider.
Most data acquisition systems offer a dedicated rpm channel, which records engine revs a set number of times every second. Just as with the speed channel, the rpm data can be plotted against distance from a beacon or start/finish line, showing engine speed at any point on the track. An rpm trace reveals plenty with just a quick glance: maximum rpm used on each straight, minimum rpm in each corner and where the rider is upshifting and downshifting. This information can be used to make a gearing change-whether it is a swap in sprockets to alter the final drive ratio or an internal ratio change-and optimize engine rpm over the course of a lap. As well, improvement may be found as easily as by pointing out to the rider that rpm is low or high in a certain corner and he could benefit by using a different gear.
Now that we are dealing with two channels-speed and rpm-the data can be further manipulated using math channels to yield even more information. Most systems' software allows the user to create an additional channel that is based on a mathematical function working on one or more existing channels. For example, knowing engine rpm and wheel speed, it's possible to use a math channel to find what gear the bike is in at any given time and display the gear position graphically or numerically. Some analysis software packages such as AiM Sports' Race Studio 2 include a gear-position channel that makes assumptions for internal and final gearing, meaning there's no need to input each gear ratio or sprocket size.
We'll come back to math channels in future installments, but for now consider some more possibilities: Wheelspin can be displayed in graphical form by subtracting front-wheel speed from rear-wheel speed, or acceleration and braking forces can be calculated from speed. As more channels are added, math channels can combine and manipulate two (or even more) channels to more easily show a certain characteristic.
Another useful tool for evaluating rpm data is the histogram. Instead of graphing rpm (or any channel, for that matter) over time, a histogram plots data as the percentage of time that it occurs within a specified category or range. For example, an rpm histogram could show that rpm is between 10,000 and 11,000 rpm for 10 percent of the lap; between 11,000 and 12,000 rpm for 15 percent of the lap; between 12,000 and 13,000 rpm for 12 percent of the lap; and so on. This can indicate at a glance how the rider is managing rpm. If the engine makes most of its power between 10,000 and 11,000 rpm, for example, and the rider is not maximizing that band as shown on the histogram, an overall gearing change may be prudent.
The case studies presented in the accompanying screen captures show more detail about rpm traces and histograms. In our next installment we'll discuss adding and evaluating even more channels.