*5.3. British Pendulum Test Rig*

The last device reported in this review is the British Pendulum (BP), widely accepted as a device for both field and laboratory friction testing. The BP test is described in ASTM E303 [85] as a laboratory testing method to find the skid resistance of pavement surface. It is a low-speed (<10 km/h) test which is related to surface micro-texture of road surface. A typical commercial device is shown

in Figure 25, with its main components. In many researches, BP is used to perform the asphalt characterization [86,87], while this review is focused on the devices used to study the interactions between a tread block sample and the road surface.

**Figure 25.** A typical commercial British Pendulum.

Ciaravola et al. [88], performed an experimental investigation of contact between tyre tread and rough surfaces by means an evolved version of a standard BP, developed starting from a BP at the Technical Centre Europe Bridgestone and customized at Department of Industrial Engineering, University of Naples Federico II (Naples, Italy). Later, Arricale et al. [89] performed an experimental investigation on tyre/road friction, between a tread block and real asphalt specimens by means an improved version of the British Pendulum developed by the UniNa Vehicle Dynamic Research Group, also called BP-EVO. The device showed in Figure 26, conserves the main components of the classic pendulum and is also equipped with a series of sensors allowing to further enrich the measurement dataset.

**Figure 26.** The British Pendulum Evo.

In detail the BP-EVO is composed by:


The main technical specifications are showed in Table 14.



The initial temperature of the tread sample can be varied up to 120 ◦C by means of an industrial heat gun and measured by an infrared pyrometer. The contact pressure can be varied using different springs. The BP, compared to the testers shown in this review, is certainly the easiest to use and, despite its simple layout, it offers the possibility to be employed in both dry and wet conditions adopting real asphalt and tread samples as a counter face. Since the pendulum is not driven by a motor, the sliding speed depends on the drop height; therefore, it is not possible making measurements in a wide range of sliding speeds. In addition, it should be noted that the range of sliding speeds may vary depending on the characteristics of the tread and the surface. For example, working with rough surfaces and tyres with high performance in terms of friction value, it is impossible to perform test at particularly low sliding speed. The reason is that, at low speed, the sample is stopped when come in contact with the surface, not allowing the friction measurement.
