The paper presents the measurement of the relaxation length of road racing bicycle tyres. In the paper the relaxation length is given as the ratio between cornering stiffness and lateral stiffness of the tyre. Tests were performed with VeTyT, a test-rig specifically designed for measuring the lateral characteristics of bicycle tyres. The results from road racing bicycle tyres of two different brands are discussed. Then, a comparison is presented between of 26 mm and 28 mm wide racing tyres. The tyres were tested both on a flat track and on a drum of 2.6 m diameter. The relaxation length for tests on flat track resulted to be on average 15% higher than the ones on drum, for the same vertical load and inflation pressure. In addition, the large role played by inflation pressure on the relaxation length was discovered. Since the relaxation length may affect the bicycle dynamics, the study provides the first quantitative information for the further development of safer and more performant bicycles.

Tyre characteristics can strongly affect bicycle dynamics. In light of this, proper test-rigs are required to accurately measure tyre parameters. The paper presents a review of the methods and devices developed for the experimental characterisation of bicycle tyres in the lateral direction. The main aspects of the known test devices are described, highlighting the respective features. The technology of test-rigs for bicycle tyre parameter measurement seems to be just beginning.

The paper describes how internal pressure, vertical force, speed and rolling surface temperature may affect the mechanical characteristics of a road racing bicycle tyre. The results were obtained from an experimental test campaign performed with VeTyT, a test-rig specifically designed for measuring the mechanical characteristics of bicycle tyres. The static deflection of tyre for different inflation pressures and vertical loads was measured to determine the static tyre vertical stiffness. Results for tyre rolling on flat track or on a drum were compared. Dynamic analyses were focused on evaluating the effect of inflation pressure and vertical load, for two rims featured by different lateral stiffness. Then, the respective effects of speed and of temperature of the rolling surface on the lateral force were considered. Stiffer rims can ensure higher values of cornering stiffness. In addition, higher inflation pressure is recommended only for heavy vertical loads. For low vertical loads, too inflated tyre results to be less performant, i.e. to show lower values of cornering stiffness. The speed can affect the mechanical characteristics of bicycle tyres mainly for slip angles less than 1.5 degrees, while the temperature of the rolling surface is the most affecting parameter for slip angles larger than 3 degrees.

In this paper, the twisting torque of bicycle tyres is studied. The twisting torque is just the self-aligning torque for null lateral slip and non-null camber. The relationship between twisting torque and contact patch area has been analyzed. As the latter increases, twisting torque increases as well. A theoretical model to evaluate twisting torque has been implemented. Since twisting torque is mainly due to longitudinal slip in cambered wheel, increasing the contact patch area the stresses are located at a larger distance from the median plane of the contact patch. The resulting torque will be higher in magnitude. Finally, the model has been validated comparing the outcomes with the experimental data, with a mean error less than 3% for camber angles less than 10 degrees.

Bicycles will be largely exploited in city mobility, as a smart and cheap tool to achieve the goals of reducing air pollution levels and increasing the liveability of cities. Their growing popularity requires more knowledge on bicycle dynamics to prevent instability. In this context, tyres may play a crucial role, as already stated in literature (European Environment Agency, 2019, 1). This is why proper test-rigs are needed to obtain reliable tyre parameters. The paper presents Vetyt, acronym of "Velo Tyre Testing", a new test-rig specifically developed for bicycle tyres at the Department of Mechanical Engineering of Politecnico di Milano. The development procedure is described step by step, enlightening the main goals achieved. Vetyt frame was reinforced to test tyres on flat track, with vertical loads up to 550 N. After that, a new air-cooling system to keep constant the temperature of the rolling surface was added. An uncertainty model was developed on theoretical basis, and a static verification of forces recorded by Vetyt was performed. At the end, the results coming from a very first experimental campaign are presented. Lateral forces and self-aligning moments are depicted for racing road bicycle tyre, for vertical loads of 400 N and 490 N. The variation of camber angle (tested up to +/- 10 degrees) contributes to the increase in magnitude of the values of lateral force and self-aligning moment.