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The straight-line tire/road friction coefficients of three motorcycle tires designed for high-performance or sports motorcycles have been measured and compared with a representative ordinary car tire. Both peak and locked-wheel friction was measured on two different surfaces (hot rolled asphalt and stone mastic asphalt), dry and wet, at speeds between 32 and 100 km/h. Unexpectedly, a substantial difference between the friction of the car tire and the motorcycle tires was not found, and while the car tire did tend to deliver the lowest friction of the four, this was, with one exception, no more than the variation among the three motorcycle tires. Generally, on the dry surfaces peak friction coefficients of around 1.2 were found, with locked wheel coefficients of around 0.7-0.9. The exception was in the measurement of the peak friction on dry hot rolled asphalt, where the coefficient of friction of the car tire was about 0.2 less than that of the motorcycle tires.

The Mannesmann Kienzle UDS2165 Accident Data Recorder has been fitted to several vehicles in a fleet of cars in London as a trial of its effectiveness as an accident investigation tool. The characteristics of the device, which provides a record of driving for 30 seconds before and 15 seconds after an accident, are described together with the results from our trials. The advantages of such a device are considerable, in that it provides information which is either of greater accuracy than that obtained by traditional methods, or which is not otherwise available at all. This includes speed and acceleration, heading angle and the use of brakes, direction indicators and lights throughout the whole 45 second period.

The results of three inquiries of relevance to accident reconstruction are given. In the first the difference between anti-lock and locked-wheel braking on a dry surface is examined, with the finding that average decelerations with anti-lock are about 12% higher. In the second the effect of anti-lock operation on the curved yaw-mark method of speed calculation is explored; the finding is that the method is still valid, although it is possible that there is a greater tendency towards underestimation. The third inquiry is into the appearance and enhancement of tyre marks from anti-lock braking, where it is found that marks are infrequently made; they are more likely to be found on uneven surfaces, and while faintly visible marks can sometimes be seen more easily with polarised light, no way has been found of developing invisible or latent marks.

Tests have been performed to investigate how the average deceleration experienced by a motorcycle sliding to rest on its side from high speed compares with the friction measured in a low-speed drag test. This has been done both by launching motorcycles from a low platform, and by allowing them to fall to their sides from an upright position, from speeds between 32 and 90 km/h. It was found that the friction measured in the low-speed drag tests gave a value close to the high-speed sliding value. The friction was affected by the road surface texture, the presence of prominent side projections, and the wearing away of these projections during the slide. Some speed dependence was noted in the upright-launch tests which appears to be due to the “digging-in” of the machine as it falls to the road, rather than an effect of the sliding friction itself.