Just before the first race start attempt, Lewis was reminded of his starting procedures, “Release the overtake button and shift on the tone”
What does “shift on the tone” mean? Normally, a driver uses the RPM indicating LEDs on the steering wheel dash to indicate when to upshift. On a race start, there are obviously many things demanding a driver’s visual attention, most especially watching his mirrors and the cars around him. As such, spending the time and discontinuity in concentration to stop watching cars around him in moving his eyes to the steering wheel dash to watch when to upshift can be costly in mental reserve capacity and reaction time. The consequence of missing an upshift point and hitting the rev limiter is an instant loss of momentum, greatly compromising the run to the first corner. Therefore, it would be beneficial for a driver to be able to maintain visual concentration on the cars around him, but still know when to upshift.
The “tone” is an audible acoustic indicator for the driver to know when to shift, heard via the radio earpieces. The idea is simple enough, but requires detailed technical execution. A device with a programmable frequency signal generator must be connected in parallel between the voice radio and the driver’s earpieces. The shift tone system must be installed in parallel, so that if it fails, it will not interrupt normal function of the voice radio. For the unit to know what RPMs the engine is experiencing and when to generate a tone, it must be able to connect to the CAN stream of the data acquisition system for shift light control outputs. The shift lights are already set not to indicate exact engine RPM, but to compensate for a driver’s reaction time to seeing the lights and then pulling the upshift paddle before the engine has reached any given target RPM.
In the post-race interview on BBC, Lewis himself states that the average reaction time is 0.2 seconds, and decreasing that time by 0.02 seconds may be equated to a gain in track position of 0.5 to 1.0 meters at the first corner. With all drivers and teams fighting within such narrow margins of performance, this is just one of the many unique human interface devices to capitalize on.