By
Counterman
Strictly as a word, performance is defined as the act or process of accomplishing something. In the automotive world, it’s often preceded by the word high, to indicate a modification which makes a vehicle perform more like a race car, but even without, it’s often thought of in the same context.
Relating to chassis bushings and mounts, we’ll look at it in both ways. The common link between suspension bushings, body, engine or transmission mounts is what they do and what they are made of.
Their purpose is to allow a minor or controlled degree of movement between two components, while absorbing shock, dampening noise, preventing vibration and preventing metal-to-metal contact between the two components. They can be made of rubber, polyurethane, plastic or metal depending on their application, but rubber is the primary material for production vehicles.
All bushings or mounts are designed to perform in a certain manner, depending on whether the vehicle is designed for luxury, performance or heavy-duty use. The difference in performance comes from the hardness of the rubber (or other material) used in any given component. Hardness is measured by a piece of equipment called a durometer.
Hardness can be related to many everyday objects such as a rubber band, super ball, automotive tires or even skateboard wheels. A rubber band, for example, would have a low durometer reading, while a skateboard wheel would have a higher reading. In automotive applications, not only are mounts and bushings engineered and formulated to meet a specific durometer rating, but all rubber components utilize this scale during engineering, as well such as door seals and O-rings.
Chassis performance, when relating to it in terms of the way any vehicle was designed and built, can be affected by the quality and type of replacement components. Manufacturers that follow original equipment (OE) standards when manufacturing replacement components do so with the intent that the replacement components will be equal to the OE in quality and performance.
This is important because the majority of vehicle owners want their vehicle to perform as it did when new. If the rubber in a replacement component is of a different hardness, a vehicle may not handle or ride as well, or there could be increased vibration transferred from the suspension or drivetrain into the cabin. It all depends on the durometer rating of the rubber.
On the flip side, vehicle performance may improve with different bushings and mounts, which leads me to the high-performance side. With suspension, a common modification is to install polyurethane bushings in place of the OE rubber. The polyurethane bushings have a higher durometer rating, which means they are stiffer than rubber. This keeps suspension components in strict alignment during suspension movement and cornering, which adds up to improved handling. But you sacrifice comfort, noise and vibration levels at the same time.
Polyurethane engine and transmission mounts can improve throttle response and acceleration by preventing excess drivetrain movement, and they handle a greater level of stress, but again you will sacrifice comfort, noise and vibration levels at the same time.
Polyurethane is used for these high-performance applications because it’s easier to customize a specific durometer rating with polyurethane than it is rubber, and therefore a higher rating can be easily attained. Plus, it is more durable and longer lasting than rubber, and it’s not affected by temperature, dirt or oil, all which plague rubber components. Certain oils can affect poly over time, but it takes extended exposure and is uncommon for the most part.
An interesting addition to the mount category has been the modern technology of active engine mounts. Active engine mounts have hydraulic fluid filled chambers inside. They are controlled either by electronics or vacuum, the most advanced of which are ECU-controlled.
The amount of dampening inside the mount is changed to meet operating conditions. With this technology, these mounts can offer comfort, low noise and vibration, along with acceleration and high-performance benefits. It’s the best of both worlds.
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