Racing bicycle tyres: experimental indoor evaluation of relaxation length

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.