How do you know what to believe when every source lays claim to having the most durable and best riding leaf springs? Some suppliers suggest that they have reinvented the wheel. Actually, there have been no light truck spring design breakthroughs in quite some time. Comprehending how spring characteristics differ requires an understanding of spring rate. Rate, in the simplest sense, is a measurement of the load required to compress the spring a given distance. In other words, it is a gauge of spring strength and flexibility. "X" amount of rate is required to support "X" amount of weight. Rate, and rate curve, is influenced by several factors including: material grade and thickness, individual leaf plate length, leaf end configuration and interleaf friction.
Standard leaf springs - With most standard springs, the spring rate has been reduced, as much as possible, to emphasize suspension travel and a more compliant ride. The different design elements can include thinner leaf material, tapered leafs, military wrap eyes and / or spring inserts.
Heavy Duty leaf springs - These leafs are generally used for taller lift applications on older model trucks, and they are designed to handle the associated abuse. Heavy Duty springs are also recommended for use on heavier-than-normal rigs. Expect ride quality to be somewhat firmer than stock.
- Optimum rate curve - These springs feature a multi-leaf pack (up to eleven leaf plates) that produces a much flatter spring rate curve. Rate curve is best described as a map of the load required to compress a spring throughout its travel cycle. A smooth, linear rate curve - one without drastic rate spikes - is one of the primary keys to good ride quality. Think of it this way... as the number of leaf plates increase, the load that each plate must absorb is reduced.
- Less friction equals better ride- On vehicles that have springs on top-of-axle (like the Ford Super Duty), using a thick spring pack means that less arch is required to attain a given lift height. A spring design with reduced arch generates less inter-leaf friction. Anti-friction pads, placed between each leaf plate, further reduce friction.
- Military-wrap eyes - Some springs feature military-wrap spring eyes. With military-wraps, the second leaf plate wraps around the spring eye (called the main leaf) to form a double-wrap. This design element transmits less stress to the main leaf during extreme articulation. It also lessens the odds of spring separation in case of main leaf failure, and provides greater strength, support, and durability as a whole. Factory type rubber eye bushings are used for quiet operation and superior durability.
- Spring clips - Clips prevent the leaf plates from "fanning out" laterally. Springs can utilize U-clips or pinch clips. U-clips allows for less restrictive movement (there's the "less friction" thing again), and more leaf plate separation to promote articulation.
- Proper travel control - If a spring actually travels (like it should), compression travel control is crucial. How much compression travel is allowed, and how abruptly this downward travel is stopped, is yet another important factor in the ride quality equation. With most manufacturers, compression travel management is a consideration.
Progressive rate coils - Most coil springs have rates that are constant; if it takes 400 pounds to compress the spring the first one inch, another 400 pounds will compress it the second inch, and so on. With a progressive rate coil, the initial couple of inches of compression requires less rate than the remainder of compression. This improves your "Sunday drive" ride quality, yet rate increase when you're in "Banzi mode". With progressive rate coils the first few coil wraps are more closely spaced than the remaining coils, or the entire spring is slightly conical (cone-like) in shape.