A driver's preference for one of two different vehicle models that have the same measurable acceleration may be explained by complicated factors such as styling, NVH or ergonomics. If the vehicles have identical appearance but different levels of engine tune, discrimination would probably be due to the measurable difference in performance although other factors cannot be entirely discounted. If however, the assessment is made of vehicles with identical appearance and identical performance then any preference is attributable to an area of human assessment that has been termed subjective performance.
This paper discusses the first step in a qualitative approach to the analysis of driver perception of vehicle performance and more specifically investigates subjective performance. The proposed model ascribes distinct components such as induced and perceived performance to the total subjective performance rating.
The model is based upon the analysis of the influence on driving behaviour of a single powertrain component (pedal to throttle progression) that previous studies have shown to correlate strongly with subjective performance. Parameters associated with this component were varied by use of a vehicle fitted with a drive-by-wire system (electronic throttle) and were assessed using a novel application of paired comparisons during a test format involving specific manoeuvres and free-driving. Any change in the continuously recorded behaviour of the driving subjects was attributed entirely to these parameters and was treated as evidence of induced performance; conversely, high ratings that arose without a significant change in driving behaviour were due to perceived performance.
In drawing this distinction between modifications which encourage the driver to drive with greater levels of acceleration and speed and those which make the car feel more powerful without a corresponding change in driving style, it is hoped to provide guidelines to direct powertrain development towards the most effective routes for improving subjective performance without necessarily increasing vehicle performance.