Torsion Spring Sizing and Replacement

Four Numbers, Taken Before Anything Is Ordered

A torsion spring is defined by four things. Wire diameter, inside diameter, overall length, and which way it is wound. Get all four right and the door balances. Get one wrong and it does not, no matter how carefully the rest of the job is done.

That is the whole reason this page exists. Sizing a spring is not difficult work. It is specific work, and it does not overlap with any other trade, which is why an experienced builder can install a spring perfectly well and still install the wrong one.

How the Measurements Are Taken

Wire diameter. Measured with a caliper across twenty coils held tight together, then divided. Measuring a single coil is not accurate enough, because the differences between common gauges are small and the door notices them.

Inside diameter. Usually stamped on the winding cone, and cross checked against the shaft. Two inch and one and three quarter inch are both common on residential doors here, and they are not interchangeable.

Length. Taken with the tension fully off, coil to coil, not including the cones. A wound spring reads short.

Wind direction. Confirmed by looking at how the last coil leaves the cone, and by which end of the shaft it sits on. A left wind on the right hand side will fit, wind up, and then unwind itself in service.

Why Copying the Old Spring Is Not Enough

The assumption behind matching an old spring is that the old spring was correct. On a door that has been repaired once or twice already, that assumption is often wrong. Somebody fitted what they had on the van, the door has been slightly heavy or slightly floaty ever since, and the owner simply got used to it.

Measuring takes a few minutes. It also catches the doors where the spring is right but there should be two of them, and the doors where a previous replacement quietly dropped the cycle rating.

Cycle Rating Is a Choice, Not a Given

A standard residential spring is rated for around 10,000 open and close cycles. A high cycle spring, made from heavier wire on a longer body, roughly doubles or triples that.

For a household that opens the door four times a day, standard is fine and lasts many years. For a door that is also the main entrance to the house, opening ten or twelve times a day, standard wire is a false economy and we will say so before you spend anything.

The Weight Question

If a section of the door has been replaced, or the door has been insulated, or a new steel back has been added, the door does not weigh what it used to. The counterbalance has to be recalculated against the actual current weight rather than against the spring that used to be there.

This is the single most common reason a door that was recently repaired still feels wrong. The spring was reused when it should have been resized.

After the Spring Is In

The spring is wound to the calculated number of turns rather than to feel. Then the opener is disconnected at the release cord and the door is lifted by hand.

A correctly counterbalanced door will stay roughly where it is left at waist height, drift only slightly, and take very little effort to move through its travel. If it drops, it is under sprung. If it rises on its own, it is over sprung. Either way the winding bars go back in and the turns are adjusted before power is reconnected.

Only after the door passes by hand does the opener go back on, and then the safety reverse and the photo eyes get tested to the UL 325 requirement, because an opener that has been fighting a heavy door has often had its force settings wound up by somebody trying to make the symptom go away.

Call (657) 633-1877 and we will measure before we quote.