Shift point

Justin Lindsay wrote these little tips about shift points back in 2013. It something never expires.

There is a quick and easy way to determine you are up-shifting too early, too late, using the longitudinal acceleration graph, and a ruler. Sorry if this gets long-winded, it’s taken from one of my eBooks on race-car telemetry, but here’s what you’ll need to know:

Shift points are not at the same RPM for each gear, if you have ever been told to shift just after the engine’s torque peak then that advice was wrong. The right shift point depends as much on gearing as it does on engine torque. Using the longitudinal acceleration channel you don’t need to worry about any calculations, just look for the intersection points of the trend lines.

If you log RPM data then you can estimate the right RPM by cross referencing the intersection point with the revs. If you don’t have the RPM channel then experiment with different shift points during practice and then correlate that with the data.

Correct Shift Point

The right point to up-shift is the point at which the longitudinal acceleration of the car in the current gear is equal to the longitudinal acceleration that can be achieved in the next highest gear. This is true regardless of the engine characteristics or gear ratios.

At this point if the driver continued to hold the lower gear the acceleration of the car would become less than
the acceleration that could be achieved in the next gear. If instead the driver up-shifted before this point then the
greater acceleration in the lower gear would be given up for less acceleration in the higher gear.

In the longitudinal acceleration channel the correct shift point can be seen by drawing lines on the acceleration trend for each gear. Extending those lines to intersect reveals the best point to up-shift.

In the graph below if the lines were extended they would intersect in the middle of the upshift, the driver shifted at the right RPM.

Early Up-shift

If the driver up-shifts early then acceleration potential in the lower gear is lost in favor of less acceleration in the higher gear.

The close up in the graph below shows the driver’s upshift point occurs before the trend lines intersect. The driver has shifted too early. In this particular example the RPM data showed the driver upshifted 200 rpm too early.

 

Late Up-shift

If the driver up-shifts late then acceleration potential in the higher gear is lost in favor of less acceleration in the lower gear. 

The close up in the graph below shows the driver’s upshift point occurs after the trend lines intersect. The driver has shifted too late.

 

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