Critical Speed Yaw Mark Calculations with and without Electronic Stability Control

More information

Main author

Lambourn, R.

Co-Authors

Jennings, P.; Knight, I.

Type of media

PDF

Publication type

Lecture

Publication year

-

Publisher

18. EVU Conference, Hinckley

Citation

Lambourn, R.: Critical Speed Yaw Mark Calculations with and without Electronic Stability Control. 18th EVU Conference, Hinckley (UK) 2009

English, 27 pages, 17 figures, 13 references

A programme of experiments has been carried out with a car fitted with an electronic stability
control (ESC) system to find what tyre marks are laid on the ground, whether they display any
features which can be taken as an indication that an ESC system is active, and whether the method
of speed calculation from the curvature of the tyre marks can be employed. The car was fully
instrumented and the ESC system could be turned off.
Four manoeuvres were employed: an asymmetric sine-steer, in which the car, in neutral, was steered
first in one direction and then more sharply in the other, before straightening up; a similar manoeuvre
in which the driver held the steering on until the vehicle had come to a halt; a step-steer, in which
the car was suddenly steered sharply to one side; and a step steer in a turn with throttle release
(sometimes called “lift off”), in which the car was driven fast in a circle, and then steered harder in
the same direction while releasing the throttle.
In each of these manoeuvres curved tyre marks were produced, displaying some lateral striations
or scratches indicative of a side-slipping of the tyres. However, the nature of the two surfaces used
for the experimentation was not such as to show the marks and any detail within them very clearly.
The angle of these striations across the tyre marks is known to have some correlation with the
amount of braking applied to a wheel; however, in the various runs no particular feature could be
found which would enable an investigator to say that the vehicle making them had been subject to
ESC intervention. In those runs where it was known that the ESC system had been activated, the
angle of the striations and the degree of yaw could be matched to the operation of the ESC, but, had
the ESC activity been unknown, these features could equally have been due to the manner in which
the vehicle was being driven.
The calculation of the speed of the car from the curvature of its tyre marks was found to be
unaffected by the operation of the ESC. However, it was noted that overall, the result was a significant
underestimate when the coefficient of friction of a sliding tyre was used, and that when the peak
coefficient of friction was used, a much more accurate result was obtained.