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 same difference was not found in the locked-wheel friction on the dry hot rolled asphalt.
Some observations are also made on the reduction in the coefficient of friction when the tires wear through to the cords of the carcass, the amount being noticeable but only in the region of 0.2.
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