Struts vs Shocks and How to Test
Modern vehicles benefit from many technological and engineering innovations designed to make them safer and more reliable. In addition, most modern cars, trucks, and SUVs provide drivers with an extremely smooth and comfortable ride, especially when compared to the rough ride common with early motor vehicles. The smooth ride is caused in large part by two key components: shock absorbers and struts.
Shocks and struts, including air shocks, have several key functions, including maintaining contact between the tires and the road, preventing the car from leaning and swaying during turns, and absorbing the impact of a speed bump or pothole. However, while both shocks and struts are key to vehicle safety and comfort, they are two distinct parts.
The difference between shocks and struts is described in the following sections outlining the functionality of both parts, the features distinguishing them from one another, and signs indicating they should be replaced.
What Is A Shock Absorber?
The shock absorber is the first line of defense against cracked pavement, rocky dirt roads, and other uneven surfaces. Contrary to popular opinion, shocks do not actually support the weight of the vehicle, but they slow down and reduce road vibrations of the road by a process known as dampening. In essence, a shock absorber is similar to an oil pump located between the frame of the car and the wheels. The key components of the shock absorber are piston, coil, and hydraulic fluid. When a car’s wheel dips, the shock initiates a compression cycle, and a piston exerts pressure on hydraulic fluid in the upper chamber of the device. The fluid serves to slow the coil as it relaxes back into place, helping prevent what the driver might describe as a bumpy ride.
What Is A Strut?
A strut integrates numerous suspension parts, including a shock absorber, into one assembly. These parts include the coil spring, the spring seats, the strut bearing, and the steering knuckle. Essentially, struts are advanced shock absorbers that have a couple additional functions. For example, the coil spring can support the weight of the vehicle and adjust to road irregularities like bumps, hills and valleys. In this regard, the strut functions as a standard shock absorber. However, the strut also serves as an integral part of the suspension system as well. The strut is mounted directly to the vehicle on one end, and on the other end it is attached to the vehicle’s suspension. Specifically, the struts connect the upper bearing to the lower ball joint so that the entire assembly can pivot when the vehicle is turned in any dir ection.
Shocks Vs. Struts
While shocks absorb impact, struts function to support and control the vehicle in motion. These two parts differ not only in terms of their specific functions but also their location in the vehicle. Most cars feature struts on the front and shock absorbers at the rear. Because struts are more complex, they are more expensive. Drivers should have their shocks and struts checked every 25,000 miles. Most factory recommendations advise a replacement after 60,000 miles.
How Shocks and Struts Affect Safety
The Royal Automotive Club (RAC) tested the effect on stopping distance at 50 mph and 70 mph, with automobiles fitted with rear shocks that were at 100 percent and 50 percent efficiency. The results were significant: a vehicle traveling at 50 mph stops an average of 12.3 feet shorter with new shocks. The benefit is comparable when the car travels at increased speeds. A vehicle traveling at 70 mph stops 22.6 feet shorter than a car with only 50 percent left in the shocks. The results of this particular test are clear: newer shocks mean safer vehicles. Therefore, drivers should pay attention to the signs of worn shocks and struts and have their car, truck, or SUV maintained regularly.
How To Tell If Shocks or Struts Need Replacement
There are many different indicators of worn shocks and struts, and all of them relate to the handling and braking of the vehicle in motion. Drivers should pay close attention to these factors, as worn shocks and struts are both a nuisance and a potential safety hazard. In terms of the feel of the car, vehicles that provide an excessively bouncy or stiff ride probably suffer from inadequate shock and strut support. Also, if the car has trouble taking tight corners and sways during turns, the suspension component of the strut may be worn down significantly. When applying the brakes, if the car bounces back and forth instead of coming to a quick stop, the shocks may be damaged. Another telltale sign of spent shocks is if the vehicle’s nose-dives down toward the ground once the car comes to a complete stop. In addition to these indicators, drivers can inspect their tires for visible signs of wear and tear. Specifically, if the tires have uneven wear patterns or flat spots on the surface, the problem is often related to worn shocks.
How To Test for Worn Shocks
While auto professionals have sophisticated equipment to test shocks and struts, drivers can apply the bounce test to a stationary vehicle in their garage or driveway to test the amount of life left in these parts. To perform a bounce test, push down on the rear fender of the vehicle and rock the vehicle up and down several times, and then release pressure. If the vehicle makes just one more bounce on its own before settling down, the shocks are in proper working condition. However, if the vehicle bounces several times before coming to a complete stop, the shocks or struts may need to be replaced.
One additional factor to pay attention to is the sound of the vehicle while it is bouncing up and down. If there is a knocking or tapping sound, it probably means that there is a loose piston or worn piston shaft bushing.