Add-a-leaf

Also called AAL, add a leaf, extra leaf, helper leaf

An add-a-leaf is an extra steel leaf inserted into an existing leaf spring pack to raise the back of a truck and stiffen it for load, as a cheap alternative to replacing the pack.

What is an add-a-leaf?

A leaf spring is a stack of curved steel strips, called a pack, bolted together and clamped to the axle. The number of leaves and their thickness set two things at once: how high the truck sits and how much load it takes before it squats. An add-a-leaf is one more leaf pushed into that stack. It costs a fraction of a new pack and it can be fitted in a driveway.

You buy it for one of two reasons that get confused with each other. The first is ride height: the back of the truck has sagged, or you want an inch or two of lift to level a front lift. The second is capacity: the truck squats under a camper, a drawer system and a full water tank, and you want it to sit level loaded. An add-a-leaf does both, but it does them by making the spring stiffer, which is the part people underestimate.

What it costs you

Ride quality, first and most obviously. A stiffer spring with the same load on it moves less, so more of the trail comes through the seat. Empty, the back of the truck gets harsh and skittish, which is exactly the condition most trucks spend most of their life in.

Then there is what it does not fix. Tired spring steel has lost its arch and its rate. Adding a leaf to a worn pack props the height back up without restoring the pack, and the result is a spring that is both saggy and stiff. If the goal is to carry weight properly, a replacement pack designed for the load is the answer, and builders who have lived with both usually say so.

Patrick's first-generation Tacoma is the ordinary version of this decision: he names heavier replacement springs as future work to handle the truck fully laden, without having published what it weighs.