Influence of tyre pressure and vertical load on coefficient of rolling resistance and simulated cycling performance

The coefficient of rolling resistance (C-r) for pneumatic tyres is dependent on hysteresis loss from tyre deformation which is affected by the vertical force applied to the tyres (F-v) and the tyre inflation pressure (P-r). The purpose of this paper was to determine the relative influence of five different levels of P-r and four different levels of F-v on C-r and to examine the relationships of C-r with P-r and F-v during cycling locomotion. F-v was modified through carriage of additional mass by the subject. C-r was determined with the coasting deceleration method from measurements performed in a level hallway. Iterations minimizing the sum of the squared difference between the actual deceleration distance and a predicted deceleration distance were used to determine C-r. This latter distance was computed from a derivation based on Newton's second law applied to the forces opposing motion. C-r was described by a hyperbolic function of P-r (C-r = 0.1071 P-r(-0.477), r(2) = 0.99, p < 0.05), decreasing 62.4% from 150 kPa (C-r = 0.0101) to 1200 kPa (C-r = 0.0038). F-v was related to C-r by a polynomial function (C-r = 1.92.10(-8) F-v(2) - 2.86.10(-5) F-v + 0.0142, r(2) = 0.99, p = 0.084), with an added mass of 15 kg (C-r = 0.0040) resulting in an 11.4% increase in C-r compared with no added mass (C-r = 0.0035). From this study, it is concluded that the relationships of P-r and F-v with C-r for cycling are non-linear. Furthermore, a simulation model shows that changes in P-r and F-v of the magnitude examined here have an important effect on competitive cycling performance.