Do more leaves mean more capacity?

Generally yes. More leaves, or thicker leaves, raise the rated capacity of the pack. As a common pickup example, a four-leaf rear pack might carry around 2,600 lb where a seven-leaf pack on the same truck carries around 3,300 lb. The trade-off is ride quality: a higher-capacity pack rides stiffer when the bed is empty.

What is the difference between single-stage and two-stage leaf springs?

A single-stage pack works as one set of leaves across its whole range. A two-stage pack has a second set of leaves that only engage under load, so the truck rides on the softer first stage when empty and picks up the second stage as weight comes on.

Should I buy higher-capacity springs than stock?

Only if the truck actually carries the load. Match the spring to the weight you haul regularly, not the weight you might haul once. A heavy-duty pack under an empty bed rides rough, and an underrated pack sags and fatigues early. Constant heavy loads justify the upgrade; occasional loads usually do not.

Leaf spring guides

Leaf count, capacity, and ride: how to read a spring

Forum threads argue about 4/1 versus 7/1 packs every week. The engineering behind it is simpler than the arguments. Here is how to read the numbers and match a spring to your load.

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A four-leaf spring pack next to a seven-leaf pack at the same scale, the seven-leaf pack visibly thicker, with one weight icon under the smaller pack and two under the larger. — Same mounting points, different working range. The thicker stack carries more before it runs out of travel.

More leaves, or thicker material, raise the capacity of the pack. A common pickup example: a four-leaf rear pack rated around 2,600 lb against a seven-leaf pack rated around 3,300 lb on the same truck. Same mounting points, different working range.

The trade-off is ride. A pack built to carry weight is stiff without it. Owners who upgrade to a heavy-duty pack and drive empty most days feel every seam in the road. That is not a defect either. It is what carrying capacity feels like with nothing in the bed.

You will see pack descriptions written like 4/1 or 7/1. The first number is the main leaf count, the second is a helper leaf that engages under load.

A single-stage pack works as one set of leaves across its whole travel. Simple, predictable, and right for trucks that carry similar weight most of the time.

A two-stage pack adds a second set of leaves that sit idle until load compresses the first stage onto them. Empty, the truck rides on the softer first stage. Loaded, the second stage picks up the weight. Our catalog lists the stage type on every part page, next to leaf count and material size.

Two-stage leaf spring diagram: the main pack above, an arrow pointing down to the shorter second-stage leaves, and two smaller states below showing the gap open when unloaded and closed under load. — The second stage sits idle until load compresses the main pack onto it. Unloaded, the gap stays open; loaded, the stages work together.

Three pickup trucks in a row: one with an empty bed, one carrying a service body, and one towing a trailer. — Empty most days, loaded every day, or towing on weekends. Each one specs differently.

Restoring stock behavior: the truck sagged with age and you want factory ride height and capacity back. Replace like for like. Same leaf count, same rating.
Constant heavy load: a service body, a camper that never comes off, tools that live in the bed. Spec the pack for that constant weight. This is where higher leaf counts earn their keep.
Occasional towing or hauling: mostly empty, sometimes working. Stay close to stock capacity and consider a two-stage pack rather than jumping to a stiff heavy-duty single stage.

Every part page in our catalog lists leaf count, stage, material size, and measurements from our engineering records. If your situation does not fit a category, tell us the truck and the load. Specifying springs is what we do all day.

APM manufactures leaf springs in its own plants and has since 1971. The capacity and measurement data in our catalog comes from the factory that builds the spring, which makes matching a pack to your truck a data problem instead of a guessing game.

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Leaf count, capacity, and ride: how to read a spring

What leaf count tells you

Single-stage and two-stage packs

Spec the spring for the load you actually carry

Built by APM, specced from factory data