Chapter 1: ACCELERATION

In motorsport to extract the best performance from an engine around a race circuit, it is necessary to match gear ratios in the gearbox to both the engine and the circuit. The aim being to have the engine in the right gear running in its power band high in the rev range for as long as possible. Years ago when road cars had 3 speed gearboxes, race cars had 5 speed boxes to allow the driver to keep the engine "on song". Road cars eventually followed suit, gaining five speed gearboxes, but for different reasons. The family car has a much broader spread of gear ratios, a very low first gear for getting the car off the mark or up steep driveways when fully laden, a low second gear, widely spaced third and fourth gear and a very high fifth gear to allow the car to travel at highway speeds with low engine revs. The differences between each gear ratio (first to second, second to third, third to fourth) also vary considerably. As such the old driving technique of revving the engine to red line in each gear before shifting is no longer the best method of extracting maximum acceleration from a typical family car. In today’s cars, with five speed gearboxes and even more so with an engine tuned for mid-range torque rather than top-end power, this shifting method can be dramatically improved. In a modern car with a well developed electronically controlled automatic transmission, if you were to hold the accelerator pedal flat to the floor and let the auto do the changing, you would notice the auto changing gears at different revs for each shift, its computer having been calibrated to shift at precisely the optimum speed for each gear ratio. If there is a wide spacing to the next ratio, the engine will be run to higher rpm before shifting. If the spacing is closer, the change will occur at much lower rpm. For a manual car the best method of acceleration is to rev to or just beyond peak power in the gear before up-shifting. After the change the engine will be right on, or just below, the point at which it develops maximum torque. By red-lining each gear the engine sounds like its making extra power but really you are only putting excessive stress on all engine component, wasting fuel and making noise. As such many cars with automatic gearboxes are smarter than a human driving a manual, although the power losses in an automatic can still be greater.

(Written by Joel Neilsen, Managing Director, Safe Drive Training)