Two Kinds Of Spring
There are two spring systems on residential garage doors and they fail in different ways, so knowing which you have is useful.
Short answer
Torsion springs sit on a shaft above the door opening and twist. Extension springs run along the horizontal tracks either side and stretch. Torsion is the better system — smoother, longer lasting and safer when it fails — and extension springs on an older door should have containment cables through them.
Telling them apart
Look above the door opening. A shaft running across with one or two springs wound around it is a torsion system.
Look along the horizontal tracks at ceiling height either side. Long springs stretched along those tracks are an extension system.
Torsion springs are shorter and thicker and sit centrally or on either side of a central bracket.
Extension springs are long and thin and visibly stretch as the door comes down.
Some doors have both arrangements on different sections, and some commercial doors have multiple torsion springs.
And a very old door may have a one-piece tilt-up arrangement with its own spring setup entirely.
Containment cables on extension springs
An extension spring under tension that breaks becomes a whip. A containment cable run through the middle of the spring and anchored at both ends keeps the broken pieces together. If you have extension springs without containment cables, that is a cheap and worthwhile addition and it is the single most useful thing on this page.
Why torsion is better
Smoother operation, because the force is applied through the shaft and the drums rather than pulled along the track.
Longer life, with higher cycle ratings available.
Better control of the door, which means less wear on the rollers, the track and the opener.
Safer failure mode, because the spring stays on the shaft rather than becoming a projectile.
Easier to balance properly, which is what makes a door feel light and an opener last.
And more adjustment available, so a door can be correctly balanced rather than approximately.
Converting and replacing
Converting an extension system to torsion is possible and is worth considering during a spring replacement or an opener upgrade.
It needs adequate headroom above the opening, which some garages do not have — in which case a low-headroom torsion arrangement may still be possible.
It is a structural fixing, because the torsion shaft bracket carries the whole door weight, so the header has to be sound.
On either system, replace springs in pairs and match them to the door weight.
Ask about the cycle rating, because a higher-rated spring is a small premium for a substantially longer life.
And have the door balanced and the opener force settings checked afterwards, which is part of the job rather than an extra.
Common questions
How do I tell which springs I have?
Above the opening on a shaft is torsion. Along the horizontal tracks is extension.
Which system is better?
Torsion — smoother, longer lasting, and safer when it fails.
What are containment cables?
A cable through an extension spring that keeps the pieces together if it breaks. Worth adding.