Spring Calc

Standard torsion-spring engineering formulas, calibrated against a reference app's outputs:

Total coils = L / wire   Active = total − 5
IPPT = K·d⁴ / (D·active) with K ≈ 2,941,200 (per-wire-size calibrated)
Weight = π·D·coils · (π/4·d²) · 0.2833
Max torque = σ(d)·π·d³/32, σ(d) = 177,500 / d^0.2045 psi
Cycles ≈ 10,000 · (max turns / working turns)4.68

Drum geometry: only the APCO 400-8 is exactly calibrated (turns 7.94 / multiplier 0.286584 on the 9'×7', 200 lb reference case). All other drums use sizes inferred from their model numbers and are approximate. Cycle estimates and Min Door Width are approximate.

⚠ Torsion springs are under extreme tension and can cause serious injury. All results must be verified by a qualified door technician before ordering or installing.