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|10-05-2015, 05:40 PM||#1|
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Tech 3 riders Marcel Schrotter and Ricky Cardus debrief following a test session at Valencia earlier this year. Even at the world championship level, riders use data acquisition to find the quickest way around the track.
For many years, race teams have used data acquisition to guide setup and help their racers find the fastest way around a particular track. Now, with the advent of GPS and the availability of sensor data from a bike’s ECU, elaborate systems are within the reach of you—the club racer and trackday rider—with either an aftermarket or OEM accessory system. That data can be a very useful tool for evaluating your riding skills and keeping tabs on your progress over time; here we will present an outline of what to look for in your own data and how to use that to go faster with more safety and less effort.
Currently available OEM systems include Ducati’s Data Analyzer, BMW’s HP Race Data Logger, and more recently Yamaha’s Y-TRAC system on the new YZF-R1M (optional on the R1). All provide GPS data as well as anything the ECU sees, such as throttle position, rpm and wheel speed, along with rider aid settings and activation signals. From the aftermarket, several GPS-enabled lap timers, such as the AiM Solo DL or Starlane Stealth GPS-3X, tap into a bike’s ECU through the diagnostic port to access ECU data. You can even put your own system together using your phone with a data app, GPS receiver (to improve GPS accuracy and rate), and ECU interface.
Because there are so many options, we won’t go into the details of each system here. That said, keep in mind that prices and performance vary wildly. If you just want lap times and basic data, something phone-based may do; if you want more channels and proper software for in-depth evaluation, expect to pay correspondingly more. Regular readers of the magazine will know that we use an AiM Solo as part of our road tests, which records lap times and GPS data and uses AiM’s powerful Race Studio 2 software package for analysis. The DL version of the Solo taps into the ECU on many models, further enhancing the Solo’s capabilities. Most of the data presented here was recorded and evaluated using AiM equipment.
This chart shows speed as recorded by GPS versus distance for a lap at Mazda Raceway Laguna Seca, with Associate Editor Bradley Adams riding our project Kawasaki ZX-6R in the 2013 AMA Daytona SportBike race. We have split the track into segments with corners numbered on the track map and across the top of the chart. Red typically indicates a right-hand turn, blue a left-hand turn, and green a straight.
There are many different ways to view and analyze data, but the most common is as a standard graph with time or distance measured from the start/finish line on the horizontal axis and the data channel (such as speed) on the vertical axis. Speed is a handy reference channel to show with any data, as the trace allows you to easily pick out corners, straights, and different sections of the track. Usually the better choice for the X axis is distance rather than time, especially if you start overlaying laps or comparing your data with that of your friends. At 30 seconds from start/finish, for example, you might be in corner six while your buddy is still in corner five; multiple data traces over a lap will steadily diverge if a time base is used. Using distance, however, you are looking at multiple laps at the same spot on the track.
Note that you may be able to view speed as measured by GPS as well as by your bike’s speedometer via the ECU, and there is an important difference. Just as your speedometer reads differently if you change gearing or tire size, or even depending on lean angle, that data will change. GPS speed is more representative of true speed and the better choice to use. We can use wheel speed for other valuable uses, however, such as comparing it to GPS speed for an indication of wheelspin.
Most software packages will allow you to create a track map, either using internal sensors or the GPS receiver. You can then break that map down into various segments for each lap of a session. Typically we don’t break the track down into each corner and straight but combine sections so that they make sense; for example, the corkscrew at Mazda Raceway Laguna Seca would be a single segment rather than two corners and a very short straight. Segment times are important in that you can find your best lap through a certain part or segment of the track and then begin to look at the other data to see what you did differently to go quicker on that particular lap. Or you can do the same using another rider’s data compared to your own. Did they brake later? Get on the throttle earlier? Or carry more cornering force? If you are using a GPS system, you can even look at actual riding lines on the track for each lap as a first step to finding those differences.
Our data software displays times for each segment of every lap of Bradley’s race at Laguna. Times highlighted in blue indicate the quickest time for that segment, while the lap marked in red denotes the reference lap with a time of 1:30.861. The segments highlighted in yellow show Bradley’s best “rolling” lap beginning at segment eight, which sums to 1:29.874; this is slightly better than the best lap timed from start/finish, 1:30.256. If you stood in what is officially turn nine with a stopwatch, this is the lap time you would have recorded.
Throttle and RPM
An important channel to keep in mind is throttle position (TPS), and this is the channel where we most often find a big disagreement between what the rider thinks he is doing and what he is actually doing. For example, many novice riders don’t have the throttle fully open on every straight, even though they swear they are “to the stop” everywhere. Another crucial thing to focus on is the trailing edges of the trace, which should drop from 100 percent (fully open) to 0 (closed) in an almost vertical line. Any curve to the trace here indicates hesitation going for the brakes, and you might need to work on finding and using a braking marker. Likewise, on the exit of the corner, the trace should rise smoothly from closed throttle to open and only open once—no open/close/open hesitations through the corner, as this improperly loads the chassis. Again, reference points help; a lot of fluctuation in the graph sometimes means you are getting ahead of yourself and trying to open the throttle too early.
The other valuable ECU channel is rpm, which can be used to help determine which gear to use in each corner or if there is time to be saved by holding a gear at the end of the straight past peak power rather than adding an upshift and corresponding downshift. While there are other channels that show various rider inputs, throttle position and rpm are the two most valuable as far as showing how the rider is using the engine and making use of its power.
With GPS we can plot Bradley’s riding line on each lap of the race; this diagram shows the riding lines for five different laps in segment one (officially turn two) of Mazda Raceway Laguna Seca. Comparing segment times for the various riding lines is one way to find the quickest line through the corner.
In addition to speed, GPS data includes lateral and longitudinal acceleration. Lateral acceleration is measured in G and reflects cornering force. A lateral acceleration of 0 means the rider is going straight with no lean angle or cornering force; the usual convention is positive lateral acceleration for a right turn with negative indicating a left turn. The maximum and minimum values depend somewhat on what tires you are using as well as your skill level, but for sport tires, 1 G (or -1 G) is a good target; for DOT race tires, look for up to +/- 1.3 G. Much below these values and you need to address your cornering speed in the middle of the corner, rather than worrying so much about the entry or exit.
In a long corner, lateral acceleration should stay at that peak in a smooth line, as this shows you are holding a constant lean angle and not standing the bike up then pushing it back down. The lateral acceleration channel can also be used to see how quickly you can go from full lean to full lean (maximum negative to maximum positive value, or vice versa) in a chicane. Transition times vary with speed—it takes longer with more speed because of increased gyroscopic forces—but if you can go from side to side in less than one second in a low- to medium-speed chicane, you are making good time. Note that here you will have to view the data trace against time rather than distance.
This chart shows speed (black), rpm (red), and gear position (blue) for a section of New Jersey Motorsports Park, with Canadian Superbike rider Jodi Christie aboard a Honda CBR1000RR during last year’s AMA Superbike event. The rpm trace, taken from the bike’s ECU, shows peak rpm in each gear and along each straight (1) as well as minimum rpm in each corner (2). Note the short-shift at the 3,000-foot mark. If rpm is sampled at a high enough rate (50 times per second here), detail such as wheelspin (3) can be seen. While many bikes do have gear-position information in the ECU, the gear channel shown here is generated using a math channel that compares countershaft speed to rpm; using this method shows graphically how smoothly (or not) the rider matches the two on downshifts (4) and will also immediately show any clutch slip.
Longitudinal acceleration can be broken down into what we normally consider acceleration (positive values) and braking (negative values). Peak acceleration is typically limited more by horsepower and your throttle/rpm use than by traction, but peak braking G is largely a function of traction. As with lateral acceleration, look for peaks of -1 G in the braking zones for sport tires and slightly more for DOT race tires. If you have trouble reaching those numbers, focus less on the initial application of the brakes and more on braking as hard as you can once the brakes are fully applied. Note that in shorter braking zones there simply may not be enough time to get to maximum braking.
Just as you can measure the speed of side-to-side transitions in the lateral acceleration data, you can (and should) also measure the time it takes to transition from full acceleration to full braking; work toward getting this to less than one second at the end of each straight. This includes closing the throttle, transitioning your hand from the throttle to the brake, and applying the brake all in one quick, smooth motion.
Data for the same section of NJMP as used in the rpm/gear chart, showing speed in red and throttle position in blue. Zero on the scale on the left indicates fully closed throttle, while 100 percent indicates wide open. The trailing edges of the TPS trace (1) should almost always be near vertical, indicating the rider is closing the throttle quickly at the end of each straight. There are some exceptions here, such as when speed on the straight is close to the corner’s entry speed and the rider turns in while still on the throttle. Note the throttle blip on a downshift (2) and that while Jodi does modulate the throttle on the exit of some corners (3), it does not close once opened at the apex.
The next step for analysis is to look at transitions such as trail braking and accelerating while leaned over. This requires combining the lateral and longitudinal channels together, either by creating a math channel or by overlaying the pertinent data traces. For a measure of trail braking, we typically look at the moment entering the corner where the magnitude of lateral and longitudinal acceleration are equal. As you arc into a corner, your braking force decreases from its maximum of about 1 G to 0 (no braking). At the same time, lateral acceleration increases from 0 (riding in a straight line) to its maximum of 1 G or more at full lean. At some point, the values are equal; on sport tires, this would ideally occur when both lateral acceleration and longitudinal acceleration have a magnitude of about 0.7 G. On DOT race tires, look for a slightly higher value, in the 0.8 range. If your intersecting point varies, work to get to this range in steps, tipping your bike into the corner with a bit more brake applied each lap, and releasing the brake smoothly as you turn in.
A lap at the Spring Mountain Motorsports Ranch 2-mile course, with Bradley aboard a stock Kawasaki ZX-10R and showing speed (black), longitudinal acceleration (blue, sometimes called longitudinal G), and lateral acceleration (red, also called lateral G). Longitudinal and lateral acceleration can be broken down into their component parts as shown on the left side of the chart. The peak values of each trace represent maximum cornering, acceleration, and braking forces. The leading negative edges of the longitudinal G trace (1) show how quickly Bradley transitions to full braking, while the trailing edge (2) shows how smoothly he releases the brake entering the turn. Note that acceleration (3) decreases as speed increases on each straight. The lateral G trace shows peak cornering force (4) in each turn and how constant Bradley keeps that cornering force (or lean angle) through the turn. In chicanes (5) the trace shows how quickly Bradley is able to go from full lean to full lean. At some point on each corner entry (6) the magnitudes of braking G and lateral G are equal (about 0.55 G here), and this number gives an indication of trail braking. On corner exits (7), the same can be applied to combinations of cornering and acceleration, about 0.7 G in this case.
On the exit of the corner, a similar intersection point should be seen for the transition from cornering to acceleration as the magnitude of lateral acceleration decreases and longitudinal acceleration increases. Again, the ideal crossover occurs at about 0.7 G for sport tires and slightly higher for DOT race tires. However, many bikes less than 600cc are not capable of accelerating that hard, so the intersection may never occur; note also that peak acceleration for any bike is less at higher speeds. As a rule of thumb, if peak longitudinal acceleration at the exit of a corner is less than that ideal intersection number, lateral acceleration at its peak should have a greater magnitude than longitudinal acceleration at the same moment in time. For example, if you are on a middleweight bike with a peak longitudinal acceleration of 0.4 G on a particular corner exit, lateral acceleration should have at least that magnitude at the same time. This also goes back to being smooth on the throttle with a single transition from off to on, and looking at these traces together can sometimes provide more help.
The power of math channels. This chart uses the same longitudinal/lateral acceleration data from Bradley’s lap at SMMR on the ZX-10R, but here we have used math channels to manipulate the data. Many data software packages offer elaborate math channel options, and this style of chart can also be accomplished using Excel or a similar spreadsheet program. Speed is shown in black. In the middle set of traces, lateral acceleration is shown as all positive values (red), and only the braking portion of longitudinal acceleration is shown, also as positive values (blue). Overlaying the graphs in this manner shows graphically how much Bradley is trail braking in each corner (the green area). Likewise, the bottom set of traces shows lateral acceleration as all positive (red) and only the acceleration part of the longitudinal acceleration data (blue). It’s much easier to visualize now where and how much Bradley is accelerating while leaned over exiting each turn (the yellow area).
While these are the primary channels to take a look at while either at the track or back at home, there is much more information that can be found in your data and applied to help with your riding techniques. Contrary to what you may think, however, a multitude of sensors is not strictly necessary; rather, it’s about using what you have access to and breaking those channels down or combining channels together to show what detail you need to see. For example, with basic GPS data from our AiM Solo, we generate an additional 15 channels of data to show specific detail. Add in additional sensors such as TPS, rpm, or suspension, and it’s possible to isolate many aspects of a rider’s technique for analysis. For a more in-depth look at data acquisition and analysis, visit datamc.org. Additionally, we quite often use data as part of our Riding Skills Series articles, which you can find at sportrider.com/sportbike-riding.
GPS: Global Positioning System, which in this case provides precise location data that can be used to determine speed, elevation and slope, and lateral and longitudinal acceleration.
Lateral acceleration: Cornering force, usually expressed in units of G with positive values for a right-hand turn and negative values for a left-hand turn.
Longitudinal acceleration: Force in the direction of travel, also expressed in units of G; positive values represent what we normally refer to as acceleration (speeding up), while negative values represent braking.
Math channel: An analysis channel created by combining multiple channels together or altering a channel using math functions.
Sample rate: How often a particular sensor or channel is measured and recorded, in cycles per second or Hertz (Hz). A higher sample rate will provide more information but requires more storage.
Telemetry: Transmitting data to a remote recorder (as opposed to storing it on the motorcycle for later download), typically using radio signals.
TPS: Throttle-position sensor, usually expressed in a percentage with 0 representing closed throttle and 100 representing fully open.
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