Tribological devices in cycling: A review

Abstract

This review, focussed on transmission efficiency and wear in cycling, presents existing friction measuring devices. It discusses their pros and cons and compares the lubrication regime they are in to the ones determined for elite cycling. Finally, it addresses technical guidelines for measuring friction forces from the transmission (F_t). F_t depend on normal load and coefficient of friction (µ). Indeed, these factors are influenced by chain tension, alignment and velocity, sprocket size, lubricants and contamination. Such parameters also have an impact on lubrication regime which influences µ. To characterise F_t, measuring devices were developed. Forty devices were classified in five categories, ranging from those closest to ecological conditions to the most specific ones. Full transmission (FTR) and single speed rigs (SSR) results can be extrapolated into real cycling, although they are less accurate as they involve more elements. Dedicated rigs engender high precision measurements on precise phenomena. All lubrication regimes are encountered in elite cycling, which is in good accordance with most of the testing conditions presented in this review, especially FTR and SSR. If Boundary and Mixed regimes are unavoidable due to the reciprocating movements of the chain elements, they should be limited. The Elasto-Hydrodynamic regime is on target as it provides low µ and wear. In conclusion, the closer the measure is to real cycling, the higher the variability. Inversely, dedicated rigs are accurate but less representative of complete transmissions. Technology improvements now make FTR and SSR reliable enough to measure small differences, along with a strong protocol.