Belt Power from Tension and Speed
The power a belt actually transmits, from the two tensions and the belt speed: P = (T1 - T2) V / 33000 hp, with V = pi D N / 12 ft/min. The point people miss: only the DIFFERENCE of the tight- and slack-side tensions (the effective tension Te = T1 - T2) does work -- the average tension just clamps the belt for grip and transmits nothing. A 250-to-100 lb drive on a 6 in sheave at 1,750 rpm runs 2,749 ft/min and passes 12.5 HP; a tighter 400-to-250 lb drive keeps the same Te of 150 and the same 12.5 HP while carrying far more total tension into the bearings. Over-tensioning buys wear, not capacity. A design aid; the belt/sheave ratings and wrap angle govern.
Formula and source
V = pi D N / 12 (ft/min); Te = T1 - T2; P = Te V / 33000 (hp).
The belt power relation P = (T1 - T2) V / 33000, first-principles as in Machinery's Handbook / the Gates Industrial Drive Design Manual, by name.
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