Leaf Springs VS Multi-Link SuspensionPosted in How To: Suspension Brakes on April 1, 2012
The debate over coil-sprung suspension and tried-and-true leaf springs is fueled by much enthusiast passion. The Jp staff is questioned about it all the time, but despite conflicting opinions, there is never really a clear winner. With so many variables to consider, personal preference and vehicle usage almost always complicates the matter.
So, with this story we’re going to cover all the pros and cons of each system and discuss how they relate to real-world wheeling. Then, like our esteemed editors, you can decide which is best for you.
Weight - Winner: Leaf Spring
True, in most cases leaf springs weigh more than coils and links, and weight is almost always considered the enemy. However, when it comes to serious off-road work, unsprung weight can really help keep your tires in contact with the ground. For regular trail use the added weight of leaf springs is favorable to combat tippy situations.
Approach and Departure - Winner: Links & Coils
Leaf springs stick out in the front and rear of the vehicle and inhibit approach and departure angle. Coil and link setups do not.
Flex - Winner: Links & Coils
With proper geometry and setup, links and coils will almost always out-flex a leaf-sprung suspension, which in many cases allows you to pick a line that avoids a tippy situation.
Simplicity - Winner: Leaf Spring
Items such as track bars and their required mounts, along with joints and control arms, add vulnerability and often require additional upkeep. Leaf springs are simple and require a lot less moving parts to function.
Cost - Winner: Leaf Spring
Coil springs may be less expensive to produce when compared to leaf springs, but any savings quickly dries up when you consider the fact that a coil-spring setup requires links to locate the axle. These links add cost and require a lot of math and subsequent testing to work correctly. Leaf springs are simpler which translates into a more cost-effective package.
Jumping - Winner: Links & Coils
Traditional leaf-spring setups do not handle aerial assaults well. This is because abrupt force loads, such as landings, require a super-stiff spring rate to absorb the energy spike and prevent bottoming out. With the additional travel afforded by links and coils the moment of impact is usually much less painful because there is more vertical travel to combat the energy spike. We’re not saying you can’t build a leaf pack to handle jumping, it just requires a more robust design to do so.
Stability - Winner: Leaf Spring
Leaf springs have a progressive spring rate that increases exponentially when compressed. As the arc of the spring flattens out, friction between leafs counteracts movement, which provides a very stable and planted feel from the driver’s seat. Coil springs are free of this friction and continue to wiggle around even when compressed. This is why coil springs feel tippy in off-camber scenarios.
Climbing - Winner: Links & Coils
The basic nature of a coil-sprung, link-type suspension eliminates any opportunity for axlewrap. With leaf springs, especially those that are soft, or are configured above the axlehousing, axlewrap can be the ever-present enemy. There are several ways to eliminate axlewrap. The most common is a torque arm device that triangulates the axle housing to the chassis. We’re not saying you can’t get a leaf-spring suspension to climb well, because you can. In most cases leafs do not climb as well as a properly set-up coil and link suspension.
Load Capacity - Winner: Leaf Spring
It’s easy to increase the maximum load capacity of a leaf spring because they are a modular design. If you need more capacity, simply add another layer of material. Conventional coil springs are constructed from a single piece of steel wire. Their capacity depends on wire diameter, the number of coil wraps, and overall length. Manufacturing limitations make it expensive to build a coil spring out of thicker wire with more wraps, so additional weight capacity adds significantly to the cost.
Ride Tuning - Winner: Links & Coils
Coils are simple to set up, especially when used with adjustable coilover shocks. Coilovers have a modular design, which makes it easy to adjust things like spring rate and ride height for a specific application. Leaf springs are a complete assembly and are not as easy to modify due to their bulk and mounting configuration. Sure, you can add additional leafs to alter spring rate, but with a coilover, you don’t even have to remove them from the vehicle to make adjustments. The modular design of a coilover is superior for tuning and packaging.
Dynamics - Winner: Links & Coils
With coil springs and link suspensions the designer has an advantage to make adjustments to things like roll center, antisquat, anti-dive, and roll-steer. However, on leaf spring suspension, these variables are much harder to control if even possible at all.
Lifespan - Winner: Links & Coils
Nobody will argue the fact that both types of springs can wear or sag over time. However, modern leaf springs have plastic insulators to combat noise and friction between the individual leafs. These parts, along with rubber bushings at each end tend to wear out over time. Links also feature rubber bushings that can wear out. While it might be negligible, for the sake of this argument, we’ll side with coil springs because they have less wear items to worry about.
What About Failures?
Any suspension component can fail. Links can bend or snap completely. Joints can break and mounts will distort with excessive force. Leaf springs are subject to sagging, or individual leafs can crack and break apart. Spring bushings can distort and deteriorate over time. So how do you judge if one suspension design is more bulletproof than another? Well, it all boils down to how it is built and used. No one setup can be deemed more reliable until all the parameters by which you are comparing are equalized. In short, you really have to evaluate suspensions from a scientific approach. Unfortunately, laboratories do not make the best place to test suspension systems. So when it comes to choosing a particular type of suspension for a multi-discipline off-road vehicle, it’s best to look around at what others are doing, and learn from their mistakes. But keep in mind that no one setup is ever perfect.