Three companies come out. All three quotes say roughly the same thing — "torsion spring replacement" — and the only figure that differs is the total at the bottom. There is nothing on any of them describing the part.

That is the problem worth knowing about, and it is not really about price. A torsion spring is not a size, it is a specification, and two springs that look identical on the shelf can be wrong for your door in opposite directions. A quote that names no numbers is a quote where nobody has measured anything yet.

A spring is a specification, not a part number

Every torsion spring is defined by four figures, and all four have to be right together:

  • Wire diameter. The thickness of the steel itself, usually between 0.2 and 0.3 of an inch. Small changes here make large changes in lifting power.
  • Inside diameter. The bore of the coil — commonly 1 3/4, 2 or 2 1/4 inches. It has to match the shaft and the cones.
  • Length. Measured along the coils of the unwound spring, cones excluded.
  • Wind direction. Left-hand or right-hand. On a two-spring door they are opposites, and fitting two of the same is a mistake that shows up immediately.

Those four exist to serve a fifth number that is not a property of the spring at all: what your door weighs. The spring is sized to balance that weight. Get the weight wrong and every other figure is precisely correct and collectively useless.

Three of those numbers are already written on the door

You can read them yourself in about ten minutes, and it changes the conversation with whoever quotes you next.

  • Wire diameter is measured, not guessed. Lay a tape along the coils, count twenty of them, measure that distance and divide by twenty. Doing it over twenty coils rather than one is what makes a tape measure accurate enough for the job.
  • Inside diameter is usually stamped into the stationary cone at the centre of the shaft, along with the manufacturer. If it is painted over, a caliper across the bore gets it.
  • Length is the one people get wrong, because a broken spring has separated and a wound spring is under load. Measure the coils only, not the cones, and on a broken spring measure both pieces and add them.

The number nobody can read off anything

Door weight has to be weighed. Most people assume it is in a manual somewhere; it is not, and the figure quoted for "a standard 16 by 7" covers a range of well over a hundred pounds depending on material, insulation, glass and how many coats of paint it has collected.

The measurement is genuinely crude: with the spring broken or fully unwound, so nothing is helping, a bathroom scale goes under the bottom section and the door is lowered onto it. That reading is the weight the new spring has to balance. It only works when the spring is not assisting, which is why it is a job-site measurement and not a phone call.

If somebody is fitting a spring to your door without that number, they are matching the part that was on there — which is only correct if the part that was on there was correct.

"We will match what is on there" is an assumption, not a measurement

It is usually fine. Doors mostly leave the factory with springs that suit them. But we see two cases often enough to check every time.

The first is a door that has been changed since it was built — insulation added, glass sections fitted, a steel door swapped for a heavier one on the same track. The spring is still the original and has been slightly undersized for years.

The second is a door that was never right. If yours has always been heavy to lift by hand, always drifted down when you stopped it halfway, always made the opener strain, then matching the existing spring reproduces a fault that has been shortening the life of everything it touches.

The quietest mistake is the wind count

A spring can be correct in all four dimensions and still behave like the wrong spring, because the tension depends on how far it is wound. The turn count comes from the door's travel — the height it moves and the drum it is wound onto — and it is not a matter of preference.

Under-wound, the door is heavy at the bottom and the opener labours on the way up. Over-wound, the door floats, will not sit down, and fights the safety reversal. Both get described by the homeowner as "the new spring is not right", and neither is a fault of the spring.

What to ask when somebody quotes over the phone

Four questions, none of which are rude, and all of which are answerable by anyone who does this properly:

  • What wire size and length are you planning to fit, and how did you arrive at it?
  • Will you weigh the door, or match the existing spring?
  • What cycle rating is the spring you are quoting?
  • Is the price for one spring or the pair, and does it include the cones and the bearings if they are worn?

A quote that survives those four questions is a quote you can compare against another one. A quote that does not name a single figure is not cheaper or dearer than its rivals; it is simply not yet a quote.

When we will not give you a number on the phone

We will quote a range on the phone all day, and we will tell you the common case honestly. What we will not do is commit to a figure for a door nobody has weighed, because the only way to be certain of hitting that figure is to fit whatever spring makes it work out.

That costs us calls. People want a number, and the firm that gives one sounds more confident than the firm explaining why it cannot. We have made our peace with it, mostly.

The short version

Ask for the wire size, the inside diameter, the length and the wind. Ask whether the door is being weighed or the old spring copied. Ask what the cycle rating is.

The numbers are not there to catch anybody out. They are there because a spring is the one part of the door that is calculated rather than chosen, and a quote that contains no calculation is describing a hope.

Garage Door Doctor’Z · (833) 991-3899 · doctorzgaragedoor.com
CSLB C61/D28 · Lic. 1138150 · Serving the Sacramento Valley since 2018.