Throttle position

A typical throttle position trace for a 600cc machine.

A typical throttle position trace for a 600cc machine at a fast track shows the throttle is wide open for a good portion of the lap. Expect much less time at full throttle on slower tracks or with larger bikes. In general, check that the throttle is wide open on every straight, and that the gearshifts are short, downward spikes.

Throttle position is the most basic and important rider input. Luckily, almost all motorcycles are now equipped with throttle position sensors (TPS) that make it an easy channel to add to your data acquisition system. This should be the first additional channel to your system, after speed and rpm. The TPS is usually found at one end of the throttle bodies, and has a three-wire connector; you can use a multimeter to find which wire has active voltage when the throttle is opened, or check in your service manual for the wiring diagram. Be sure that you connect to the correct sensor; you want to measure the rider’s throttle input, not the secondary butterflies or – in the case of Yamaha R6 and R1 models – the main butterflies.

This sensor will require some calibration to read the throttle opening as a percentage of full throttle. Depending on your system, you may be able to automatically calibrate the channel by pressing keys when the throttle is closed and then open, or you may have to actually measure the voltage and input the numbers. The sampling rate does not have to be overly high for this channel, nor will much smoothing be necessary.

These two traces, for two different riders, show almost identical leading edges for the TPS channel.

These two traces, for two different riders, show almost identical leading edges for the TPS channel. On the trailing edge, however, the blue rider’s throttle drops to zero almost instantaneously while the red rider eases off the throttle. A quick transition from throttle to brake at the end of the straight will result in a sharp drop; the slow decrease hints at indecision and lack of a brake marker.

When looking at the data, check the throttle position trace for some basic characteristics first; you’d be surprised at what even expert-level racers overlook at times. The throttle should be fully open on each straight. When the throttle is opened at the corner exit, it should stay open; watch for a dip just after the initial opening, which can represent the rider re-gripping a long-travel twistgrip. Gearshifts are shown by dips in the trace, and these dips should be short and crisp; with quickshifter-equipped bikes, the rider should not be closing the throttle to shift.

The leading edges of the throttle trace – when the rider opens the throttle exiting each corner – should be smooth. How soon the throttle is opened and how steep the trace appears varies from rider to rider, but some generalities can be made. Checking the track map and comparing where the rider is in the turn to the throttle position is helpful here; the throttle should be opened at or before the apex, and fully opened when the bike is traveling straight. A too-steep opening may indicate that the rider is too aggressive, and may benefit from opening the throttle sooner but slower. Likewise a too-shallow opening may mean the rider is opening the throttle too soon and running wide on the exit of the turn.

Just because the throttle is open, does not mean the bike is accelerating.

Just because the throttle is open, does not mean the bike is accelerating. The turn in this graph, from 400m to 1000m, is slightly uphill and taken at approximately 100mph. Note that the bike does not gain speed unit the 900m mark, when the throttle is close to 50 percent open. When dealing with TPS data, always check the track map and speed channel to see where the rider is actually accelerating out of the turns.

Some implications of speed to consider: In faster corners, more power is needed to overcome aerodynamics and the throttle will have to be opened sooner in the corner as well as more fully opened to account for this. Data shows that for a 600cc machine in a 100mph corner, as much as 30 percent throttle opening is required just to hold a constant speed. Also at work here is the effect of tire circumference: When the bike is leaned over in a turn, gearing is shortened and rpm rises; the throttle may have to be opened more as a result, especially in faster turns. When looking at throttle traces, check the speed trace also to determine when the bike actually begins accelerating as opposed to simply looking at when the rider opens the throttle.

At the end of each straight, check that the closing edge of the throttle trace is crisp and near-vertical. A quick transition from throttle to brake is critical for out-braking maneuvers, and any delay in closing the throttle indicates the rider is hesitant about brake markers. In later sections we’ll see how a brake pressure sensor or switch helps in evaluating this aspect of rider performance, but the throttle position trace on its own is a good indicator.

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