One of the new features on the updated 2012 BMW S1000RR is a "best lap in progress" function as part of the onboard lap timer. By comparing distance and time at intervals, the lap timer can determine if elapsed time to that point on the track is better or worse than it was on the best lap previously recorded. On the BMW, this calculation is performed at 100-metre intervals, and a lamp on the dashboard illuminates to indicate a favourable result.
Most data acquisition systems offer a similar feature. In fact, any two channels can be compared using a difference channel function; for example, a speed difference channel will show exactly where on the track speed is greater or less than it was on a reference lap. If the difference function is applied to the elapsed time channel for two laps, a "lap-time difference" channel can be displayed. This is essentially the same function as the BMW's best lap in progress feature, but the calculation is performed dozens of times per second instead of once every 100 metres.
Like the BMW, a light on the system's dashboard can be illuminated when the lap-time difference is positive, but in this case the feedback is almost instantaneous and constant. Additionally, the data can be output in graphical form; the lap-time difference function can show a lot of information in a simple format. Shown here is data for two laps of Las Vegas Motor Speedway's classic course, with Javelin Broderick riding a Yamaha YZF-R6. Speed for the faster of the two laps is shown in red, while speed for a lap .34 seconds slower is shown in black. The bottom trace, in blue, shows the lap-time difference between the two laps.
Most data acquisition systems offer feature similar to the BMW's, but the results can be plotted as a data channel. Here, the blue trace shows the difference in time (blue) between two laps of the track, with speeds shown in red and black.
By the convention used, if the lap-time difference trace increases, the time for the lap shown in red is improving compared with the lap shown in blue — note that at the end of the lap, the blue trace shows the overall difference in lap time, about .34 seconds. While progress over the course of the lap is fairly steady, there are a couple of anomalies that bear further investigation. In turn 3, for example (note the turn markers across the top of the graph), Javelin saves a full .3 seconds on the slower lap in one corner (the trace drops), even thought the speed traces are almost identical. The lap-time difference trace shows that a significant portion of that time was then lost on the following straight (the trace increases), but not enough to offset the advantage gained in the turn. In this case, examination of the position data showed that Javelin took a tighter line in the turn on the black lap, and although this hurt speed slightly on the straight, the tighter line overall is a better option.
The lap-time difference function is a powerful tool that shows, at a glance, how time is gained or lost over the course of a lap. These differences are sometimes very difficult and time-consuming to find in the segment data, but the lap-time difference graph can be used to quickly and easily find those areas of interest that require deeper investigation.