Torsion spring
A wound steel spring mounted on a shaft above the garage door opening that counterbalances the door’s weight as it opens and closes.
- Torsion spring
- Torsion shaft and centre bearing plate
- Cable drum
- Lift cable
- Vertical track
- Roller
- Bottom bracket — under full spring tension
A torsion spring sits on a horizontal steel shaft above the door and stores energy by twisting rather than stretching. As the door closes the spring winds tighter; as it opens the spring unwinds and lifts most of the door’s weight, which is why an opener motor of well under one horsepower can move a 300-pound double door.
Torsion systems replaced extension springs on most residential doors because they balance the door more evenly, last longer, and fail less violently. A single door usually has one spring; a double usually has two.
A wound torsion spring holds its stored energy whether the door is open, closed or already broken, which is why replacement is not homeowner work.
On a quote, a torsion spring line should name three things: how many springs, the cycle rating, and whether the lift cables are being replaced at the same time. If any of the three is missing, ask. The difference between a standard and a high-cycle spring is invisible once fitted and is the most common way to be overcharged in this trade. A technician should also test the door balance before leaving, because a spring wound to the wrong tension puts the load straight onto the opener you will otherwise be replacing next.
One more thing worth knowing before you accept a quote: a torsion spring is matched to a specific door, not to a door size. Four measurements define it — wire diameter, inside diameter, overall length and wind direction — and getting any of them wrong leaves the door either too heavy to lift or fighting the opener on the way down. That is also why fitting a heavier insulated door onto the springs that came off the old one is a genuine mistake rather than a shortcut: the springs are now counterbalancing a weight they were never wound for, and the door will be out of balance from the first day. A reputable installer prices new springs into a new door as a matter of course; if a quote does not mention them, ask whether the existing ones are being reused and why.