P = tension in belt (1-tight, 2-slack)
hp = horsepower
s = ultimate strength of belt
t = thickness
b = belt width (in)
f = coefficient of friction (leather = 0.3, rubber = 0.25 Flat belt (use .5123 for V-belts)
p = belt density (lb/in³ 0.035 for leather, 0.045 rubber)
V_s= belt speed
C_m, C_p, and C_r = correction factors for motor type, pilley size and environmental conditions.
= Angle of contact

Materials properties S_uleather ~ 250 - 400psi