Let's Get Technical: Suspension

By Tom Dobush, September 2013

Last time I wrote about the only part of your car that touches the road surface, the tires. Now I will touch on the suspension which holds those ever important tires to the road. Yes, we all know gravity plays a large role in pulling your car and its tires towards the center of the planet and subsequently keeps it stuck to the road. However, while driving down a road or through a corner the different parts of your suspension are designed to keep as much of the tire in contact with the road as possible. A healthy and properly aligned suspension is crucial to driving safety, as well as economy and performance.

Most cars today have struts, springs and dampers to cushion the ride for the passengers and absorb the vibration caused by the tires and wheels rolling over the road surface. A strut is basically an assembly of a damper inside of a spring. The springs carry the weight of the vehicle and are constantly being compressed at varying rates, which over time stresses the metal causing tiny cracks that eventually rust and deteriorate and then break. A broken spring usually makes a metal on metal scraping, popping, clunking or crunching noise. Not fun.

Dampers are intended to keep the car from bouncing on the springs when you drive over a bump or shift the weight of the vehicle turning into or out of a corner or stepping on or off the brake or accelerator. They are usually filled with a fluid that is forced through a valve inside of the damper that has a specific rate of flow effectively dulling or dampening the frequency of the shockwave sent through the tire and into the car. Different dampening set ups, when matched with various spring rates produce a lot of the feel your car has. How much of the road surface you feel is directly related to how hard or soft your springs and dampers are set up. When the dampers wear out from use or age they will sometimes leak or seep their fluid but often do not. You may notice a rougher than new ride or a bouncy ride down the road if your dampers are worn, but very often the change in ride quality is so gradual over time that it goes unnoticed.

The next order of business is the suspension geometry, most commonly made up of truss like arms that provide the pivot points intended to allow your wheel and tire to move up and down or turn left and right in a controlled manner, thus the term control arm. These control arms can go by several names for specific applications. For example some come in the shape similar to that of the letter ‘A’ and are logically referred to as an A-arm. There are also swing arms, trailing arms, connecting arms and such, hopefully you get the idea. Often nowadays to save weight and increase overall performance these control arms are made of an aluminum alloy. This is great for adding lightness but sometimes fall short on durability, especially in the Northeast. Bent arms can make a vehicle pull one direction or another or wear tires unevenly; they can also make the car difficult or impossible to align correctly and need to be replaced. These control arms are most commonly attached to your vehicle’s frame at very specific pivot points. Bushings and bolts hold most control arms to the frame, however some of these pivot points require a range of motion that can only be afforded by a ball joint, much in the same way the bones in your arm connect at your shoulder. These ball joints usually connect at the wheel hub and require grease to lubricate them and a rubber boot to hold the grease in the joint. These rubber boots wear out or crack and release the grease eventually causing the joint to wear prematurely. This ultimately allows play in the geometry that can cause all sorts of squeaks, clunks and thuds, and if they fail at speed, could cause the loss of control of a vehicle. Needless to say, healthy ball joints and control arms are very important to safety when turning your steering wheel or riding over bumps.

To keep all of this suspension pointed in the right direction, in most cases a steering rack of some type or another is used. The rack manipulates the control arms to turn left or right via a pair of tie rods that connect with another smaller ball joint to the wheel hub, one for each wheel that turns the car. When parts of this system wear out you can sometimes feel a change in the steering wheel even if only slightly.

From springs and dampers to control arms and steering gear, each individual component of your car’s suspension is tied in tightly to the overall system. Annual state safety inspections are a required for obvious reasons. But, depending on your driving style and the roads you use, seasonal or monthly check ups are not only a good idea for safety’s sake; they might also save you some cash and peace of mind over the long run!

Now you hopefully have an understanding of the most common suspension parts and how they relate to each other and your driving experience. Next time we will look at the specifics of properly aligning all of your vehicle’s suspension geometry for safety, economy and performance reasons. Look for more information in the next issue’s upcoming article. As always, I greatly appreciate your questions and feedback and can be easily reached at BavarianRocketScience@gmail.com. Thanks for reading and happy motoring!