## 883rotary Inertia Rolling And Gradient Resistances

While translatory-mass inertia calculation is relatively easy, that of rotary mass is more difficult. It is necessary to sum the rotating inertia of the separate transmission components by relating relative torque to the driving axle as T = SIaR2 - for moment of inertia I and angular acceleration a. Since wheel circumferential speed is equal to vehicle translatory velocity, an 'equivalent mass' can be considered as concentrated at the rolling radius - having the same effect on the inertia of translatory motion as the summation of individual rotary inertias. Thus effective inertia mass M = Mi2ad =SIR2 where equivalent mass M =SIR2/r2, the effective l e 1 e mass being Mi = M + M = MY where Yis termed the rotary mass factor, a valuable tool of the method. To find its value, the rotary masses are divided into parts rotating with wheels - and those rotating with power unit. The latter gain in importance in the lower ranges since Me is proportional to R2. Average values quoted in the literature for a fully laden commercial vehicle are fourth-gear, 1.09, then 1.2, 1.6 through to 2.5 in first. The value of Y is obtained from

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