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