1. Load and speed vary in discrete steps, the equivalent constant dynamic load (P) is given by,

P = {[(P_a)^p N_a a] + [(P_b)^p N_b b] + [(P_c)^p N_c c] + . . .}^1/p

where a b c, are proportions of the duty cycle at loads P_a and speed N_a, P_b and speed N_b, P_c and speed N_c, etc. and p, the bearing life exponent, is 3.0 for ball bearings and 3.333 for roller bearings.

The equivalent constant speed at which the this equivalent load operates is calculated from,

N = {N_aa + N_bb + N_cc + . . .}

2. Load and speed cycle continuously:

i) Plot for one complete cycle the value of P_v^pN_v against time, where P_v is the varying load and and p, the bearing life exponent is taken from the table above;

ii) Estimate the average value of P_v^pN_v;

iii) Estimate the average speed N_av from a plot of one complete cycle of N against time;

(iv) Calculate the equivalent constant dynamic load from:

P = {[(P_v)^p N_v]_av / N_av}^1/p