I'll be the first to admit, a nice set of coilovers is an extremely satisfying purchase. You get a big, heavy box full of shiny threaded metal parts for the underside of your car or equally suitable for mounting above your fireplace. They allow you to lower your vehicle, so everyone knows you're a hardcore car guy. If used properly, they improve your car's handling. But what happens when you get the ride height, corner balancing, and damping rates all dialed in, yet you still don't have the precision and communication you were looking for? The culprit might be a set of parts you had never even considered.
That's the big hurdle for aftermarket high-performance bushing companies like Energy Suspension and others; they may have a great product at a great price, but they aren't on every enthusiast's "must-do" list. Maybe bushings aren't sexy enough or maybe they're just misunderstood—either way, if you can handle modifications that aren't for social media likes, then let's talk viscoelastic systems.
Just about every car on the market comes off the assembly line equipped with rubber bushings. Rubber is inexpensive, offers good NVH absorption, and requires next to no maintenance until replacement—and they will definitely require replacement at some point. For the average person, the trade-off between the greater flex but lower road noise of rubber might be worth it, but if you were an average person, you wouldn't be reading this.
Technically, polyurethane is rubber. It is a synthetic rubber as is the soft black goo currently in your suspension parts, sub-frame, and engine mounts. That black rubber is made from petroleum byproducts as opposed to natural rubber gum that comes from trees. Polyurethane is a reaction polymer created in a thermoset process, like an epoxy. I could get more into the individual chemistries of both, but if you are really interested, set aside a good three hours to fall down that rabbit hole online. From here on out, Rubber will be used to describe the factory bushing material and polyurethane to describe HYPER-FLEX, the proprietary material used by Energy Suspension and other products like it.
First, why do you want to remove flex from suspension and chassis components? Flex slows down your chassis' response and causes a disconnect in feedback from the car. In tire and suspension testing, we do what is called a step-steer test. It involves driving at a constant rate of speed, quickly dialing in a specific steering angle, holding that input, and then measuring the car's response. Most cars will have an initial reaction and then a secondary reaction after everything in the car settles. While some of the settling is the tires, a great deal of it is suspension deflection. The goal is to have very deliberate initial response and a very minimal secondary, but soft suspension bushings not only take longer to settle but will deflect more, causing unwanted geometry changes. The same is true with subframes and powertrain mounts. The engine jerking one way and then the other on turn-in is what we call secondary motion and can cause anything from an unsettled feel in cornering to invoking sudden under- or oversteer. The Mercedes SLS— with its front-mounted engine, torque tube, and rear-mounted transmission—is one such car that suffers from big secondary powertrain movements, making it feel unsettled. Mercedes fixed this in the AMG GT, which uses a similar drivetrain, by offering effective yet expensive magneto-rheological drivetrain mounts that stiffen instantaneously during hard driving to reduce motion, but soften during normal driving to absorb NVH.
Designing polyurethane bushings isn't quite as simple as you might think, as we found out during our visit to Energy Suspension's headquarters in San Clemente, California. We refer to the hardness of polyurethane and other like materials using the Durometer scale. More accurately, a couple of different Durometer scales. You will see two main scales denoted by a number followed by either an "A" or "D." An average car tire will have a Durometer of 60A, while a much harder shopping cart wheel is a 50D. The two methods use the same testing method of pressing a probe into the material with an exact force and measuring deflection, but different probes and forces are used.
Even bushing manufacturers focus solely on Durometer, when in fact that is not the only thing that affects performance in terms of deflection and NVH. Think of a bushing like a mini-suspension system for the particular joint. Just like your car, there is not only the spring rate, represented by the hardness, but there is also hysteresis, or the damping ability of the material. If you have a high spring rate and no damping, you get a car that bounces around and never feels settled. If you have an overdamped car, you get poor impact absorption, but still plenty of movement. Bushings are the same, and that energy is dissipated through heat in the material. One of the few downsides of polyurethane is its coefficient of thermal conductivity, which is not as favorable as rubber. Companies like Energy Suspension can work around this by either making the material stiffer to decrease the amount of movement or by using more material to distribute the energy over a greater volume.
You can see in the accompanying photos that several of the bushings for this MK6 Golf R use substantially more material than the factory rubber bushings. This not only allows for greater energy absorption, but also for a stiffer bushing due to geometry and not just material stiffness.
During our visit, this car received an entire set, consisting of replacements for every rubber bushing in the front and rear suspension, including antiroll bars as well as the lower torque mount insert for the powertrain. Strictly speaking, it isn't necessary to do every bushing all at once, but you probably want to talk to either Energy or your chosen dealer to determine which bushings or combination of bushings is right for your particular needs.
Because of the high abrasion and chemical resistance, these polyurethane bushings will last far longer than factory rubber. If you keep them lubricated, and you probably want to get under the car every few years to do that, they are nearly lifetime parts. It is entirely possible to DIY these bushings at home, although a few will be far easier to install if you have access to an arbor press, which can normally be found for less than 100 bucks. Some are even easier to do with a hydraulic press, but most local shops will be willing to press them in for you for $20 or even a six-pack.
The results of bushings are sometimes hard to quantify. While you will see better response in handling, better communication, less wheelhop when accelerating, the actual numbers on paper aren't necessarily easy to see. For drag racing guys, you will see slightly better 60-foot times. For road racers, the extra confidence in the car will let you push harder for faster lap times. The decreased deflection will give you better handling at the limit, as well as decreasing tire wear from unwanted geometry changes. The majority of enthusiasts probably don't give bushings a second thought; the ones who do are probably doing it when the factory pieces need replacing. Those who have done bushings in the past swear by the improvements. We have to thank Energy Suspension for allowing us to shadow them while they were engineering the kit for the MK6 Golf R and giving us more insight into these often overlooked, but critical performance pieces.