Racepak G2X Data Analysis
In order to accurately record and display how fast each machine was going and where, we strapped our GPS-based data acquisition system to both vehicles during their timed lapping sessions. Some of the results are about what we expected; others, however, are a bit of a surprise. The attached graph displays speed for the car and bike over the course of one lap as we usually show in our comparison tests. New in this graph, however, is a "lap-time difference" trace-in blue-that shows a running tab on the time gap between the car and bike at any point during the lap. A positive value indicates the motorcycle is ahead of the car at that particular spot on the track; likewise, a negative value shows the car ahead of the motorcycle. Note that the lap-time difference is always positive here, indicating the bike is ahead of the car the entire lap.
As shown by the stopwatch, overall performance on the racetrack is a bit lopsided in the bike's favor. While this result was not unexpected (sportbikes are obviously much closer to their racing brethren than automobiles), what did surprise us is how well the motorcycle compared with the car in terms of cornering performance; the S 1000 RR shows more speed not only on the two straights but also in many of the corners. Even though the car is much heavier, we figured that its contact patch/electronic chassis stabilization advantage would enable it to possess higher corner speeds everywhere. Note on the lap-time difference trace that it is almost always increasing, indicating that the bike is steadily pulling away from the car, even in many of the corners. The car shows higher apex speeds in seven of the track's 13 turns, with the bike faster in six corners.
Bike, front straight: 125.4 mph
Car, front straight: 98.4 mph
Bike, back straight: 127.5 mph
Car, back straight: 104.9 mph
As shown in the speed traces on the graph, the bike pulls a huge advantage over the car on both of the Streets of Willow's straights, with more than 20 mph in hand. This equates to a savings of three seconds for the bike in just these two segments, almost half of the 6.5-second difference in total lap time.
Turn 6 segment time
Bike: 3.77 sec.
Car: 4.25 sec.
Turn 11 segment time
Bike: 3.38 sec.
Car: 3.98 sec.
These two segments account for another full second in the bike's favor, with the bike carrying more speed as can be seen clearly in the graph. Both these turns fall in the middle of a series of corners and show how the track is more open for the motorcycle than for the car. The width of the car means any chicane or switchback is correspondingly tighter for the car than for the bike, and the bike can take a straighter and faster line through the section. In the tighter Turn 11 section, the difference in speed between the car and bike is significant, but the slower speeds equate to a similar time gap as seen in the more open section that includes Turn 6.
These graphs plot lateral g-force against longitudinal g-force for the car and bike; data from an entire lapping session rather than just a single lap was used, and the traces represent the maximum combined values recorded during the session. These traces also represent the traction circle for the car and bike, and show some significant differences. The top half of the chart represents acceleration, and it's clear that the bike can accelerate harder than the car; the peak value recorded for the motorcycle is .8g, while the car reaches just over .5g. The lower half of the chart is deceleration, and here the car holds an advantage, with maximum braking of just over 1g compared to the bike's maximum of approximately .8g. In terms of lateral acceleration, the right half of the chart represents the right-hand turns on the course; the left half, the left-hand turns. On the left side of the chart, it's a draw between the bike and car with a maximum of 1.2g for each; on the right side, the bike holds an advantage with more than 1.5g compared with the car's 1.2g. Why the discrepancy? This portion of the traction circle is largely determined by performance in the Streets of Willow's banked bowl turn, where the bike can take advantage of the additional camber offered while the car seemingly cannot. In this turn, segment 8 on the data graph, the bike holds this higher lateral g-force momentarily and there is only a slight difference in speed between the car and bike. Still, this turn accounts for a 4 mph apex speed differential and a further .3 seconds gap in lap time between the two vehicles.
The four quadrants of the traction circle show combinations of lateral and longitudinal g-forces. For example, the top right quadrant represents acceleration while turning right while the bottom left quadrant represents braking into a left-hand turn. Note that the car, in addition to braking harder than the bike, is able to combine more braking and cornering forces than the bike is capable of. In other words, the car trail brakes into corners better than the motorcycle. This is also seen on the lap-time difference graph, where the car gains more than a quarter-second on the bike entering most corners.