Drivetrain losses: Spicer's data
Recall Spicer did some nice drivetrain efficiency measurements, which he published in Human Power 50, 2000. His argument is that chain tension is an important parameter, that higher tension tends to yield higher efficiency. Here's his result again: Spicer 's efficiency measurements as a function of reciprocal chain tension for each of three rear cogs My model described dissipated power rather than drivetrain efficiency. To get efficiency (ν), I take the power dissipation as a function of T and divide it by power P, where T / P = chain speed = R L = C N f L. ν ≡ 1 ‒ P dt / P = 1 ‒ (K / L) [1/N f + 1/N r + 2 (T 0 / T) (1/N f + 1/N r + 2/N d )] ‒ K d / (N d T L). Spicer says efficiency depends on T but is independent of chain speed. However, since Spicer uses a conatant N f , for him constant chain speed simply means constant C. the above equation is indeed independent of C. Furthermore, Spicer says ν is well fit by a formula ν = ν ∞ ‒ α / T for some constant ν ...