Spring convention
Spring tension calculator
Enter the spring you have on the shaft. We show the tension it builds turn by turn, the load on the cables and drums, and how to convert between a two-spring and a single-spring setup safely.
Tension at full wind
Rate per spring
36.1 IPPT
Turns to wind
7.43
Torque per spring
268 in-lb
Total torque
537 in-lb
Door weight balanced
268 lb
Wire stress
205,552 psi
Expected life: Unsafe — wire overstressed
6.68 lift turns + 0.75 preload turn = 7.43 total turns on the shaft. Rate uses the true torsion formula: E·d⁵ ÷ (10.8 · mean diameter · coiled length), with the Wahl stress correction and the wire's own tensile strength for cycle life.
Cable & drum load
Tension per cable
134 lb
Minimum cable rating (5:1)
671 lb
Tension turn by turn
| Turns wound | Total torque | Lift force |
|---|---|---|
| 0.93 | 67 in-lb | 34 lb |
| 1.86 | 134 in-lb | 67 lb |
| 2.79 | 201 in-lb | 101 lb |
| 3.72 | 268 in-lb | 134 lb |
| 4.65 | 336 in-lb | 168 lb |
| 5.58 | 403 in-lb | 201 lb |
| 6.51 | 470 in-lb | 235 lb |
| 7.43 | 537 in-lb | 268 lb |
Convert to a single spring
Each replacement spring must rate 72.2 IPPT to keep the same balance on a 7' door.
- 0.2437" × 2" ID × 14"72.2 IPPT · Unsafe — wire overstressed
- 0.2500" × 2" ID × 15.75"72.7 IPPT · Unsafe — wire overstressed
- 0.2343" × 2" ID × 11.5"72.5 IPPT · Unsafe — wire overstressed
- 0.2253" × 2" ID × 9.5"72.5 IPPT · Unsafe — wire overstressed
Results assume oil-tempered wire and a balanced door. Sizing a brand-new spring? Use the spring calculator.