Leaf Springs: Adding & Subtracting.
We’ve mentioned previously that leaf springs consist of several cambered steel blades assembled into the shape of something resembling a crescent moon. The blades become shorter from top to bottom. Prior to assembly, you will also notice that the lower, shorter blades have more of a camber than the upper longer blades.
It is common practice to stiffen a leaf spring pack by adding more blades into the pack. Conversely, removing blades will make it softer. The stiffness of a leaf spring is determined by a rather complex equation which takes into account, amongst other things, the total number of blades, the number of full length blades (normally the main blade and 2nd blade from the top), blade width, individual blade thickness, the total length of the spring pack measured along the upper surface as well as something called Young’s Modulus (elastic modulus) which is a constant for spring steel.
Generally, adding more steel to a leaf spring pack will make it stiffer. This can be done by using wider blades, thicker blades or adding more blades. Making the entire spring pack longer will however make the springs softer. Wider blades or a longer spring pack are almost never an option as they will not fit. You therefore have the choice of adding or removing blades from the existing spring pack or replacing the entire spring pack with an aftermarket replacement product.
Up-rated aftermarket replacement leaf springs have been designed from the ground up with less or more spring rate than the original equipment spring. They are also able to maintain this at the correct ride height. The entire spring pack has a different design to the original spring on the vehicle. Considerations such as load carrying ability, axle articulation ability as well as ride comfort are all part of the design process. A purpose made, well designed spring is always the better option.
Adding fresh blades into a sagged leaf spring pack should not be considered. This may work in the short term but you will eventually end up back where you started. If you absolutely cannot afford to fit a quality after market replacement set of leaf springs, always ensure that you deal with a quality spring works company.
Typically, additional blades are added as high up in the spring pack as possible. They should not be the same length as any blades on either side of them. Ideally they should be midway in length between the blades above and below them. They should also never interfere with any fitting or clips that form part of the leaf spring pack.
When removing blades from a pack that is too stiff, it is again advised to remove a blade as high in the pack as possible. In most cases this is the 3rd blade from the top. Blades that have any fittings or clips attached to them should never be removed. These fitting and clips are vital to ensure the correct operation of the leaf spring pack.