**Andrea Genovese \* , Gennaro Antonio D'Angelo, Aleksandr Sakhnevych and Flavio Farroni**

Department of Industrial Engineering, University of Naples Federico II, Via Claudio, 21-80125 Naples, Italy; gennar.dangelo@gmail.com (G.A.D.); ale.sak@unina.it (A.S.); flavio.farroni@unina.it (F.F.) **\*** Correspondence: andrea.genovese2@unina.it

Received: 22 July 2020; Accepted: 11 September 2020; Published: 16 September 2020

**Abstract:** The future evolution of autonomous mobility and road transportation will require substantial improvements in tyre adherence optimization. As new technologies being deployed in tyre manufacturing reduce total vehicle energy consumption, the contribution of tyre friction for safety and performance enhancement continues to increase. For this reason, the tyre's grip is starting to drive the focus of many tyre developments nowadays. This is because the tread compound attitude to maximize the interaction forces with the ground is the result of a mix of effects, involving polymer viscoelastic characteristics, road roughness profiles and the conditions under which each tyre works during its lifespan. In such a context, mainly concerning the automotive market, the testing, analysis and objectivation of the friction arising at the tread interface is performed by means of specific test benches called friction testers. This paper reviews the state of the art in such devices' development and use, with a global overview of the measurement methodologies and with a classification based on the working and specimen motion principle. Most tyre friction testers allow one to manage the relative sliding speed and the contact pressure between the specimen and the counter-surface, while just some of them are able to let the user vary the testing temperature. Few devices can really take into account the road real roughness, carrying out outdoor measurements, useful because they involve actual contact phenomena, but very complex to control outside the laboratory environment.

**Keywords:** friction testers; tribometers; viscoelastic materials; rubber friction; tyre
