Add-a-leafs are designed to provide an additional 1.5" to 2" of height to your vehicle with leaf spring suspension. Including an add-a-leaf will also increase your load capacity. The exact amount of lift will depend on the weight of the engine or other accessories that have been added such as a winch, heavy bumper or snow plow.
Add-a-leafs come in different lengths. A short add-a-leaf is simply added to the existing spring pack. A long add-a-leaf is inserted within the spring pack. While the addition of any add-a-leaf will firm up your ride, the longer add-a-leafs have the least impact on firmness.
Typically, longer u-bolts are not required. However, replacing older u-bolts is highly recommended.