SUV Ride Control: Shock Absorbers & Struts

By Larry Carley c2007

Sport utility vehicles (SUVs) represent a real challenge for shock absorber and strut manufacturers, as well as technicians, because of the different ways these vehicles are used. Many people who buy SUVs today essentially drive them like cars. They haul the kids to school, run errands and commute to work - and rarely if ever go off-road.

This type of owner typically wants a smooth, comfortable ride more than anything else. Of course, they're concerned about stability and safety, too. The latest SUV models that have independent front and rear suspensions with softer springs and ride control are engineered to cater to this type of buyer. Also, strut front and rear suspensions are becoming more popular on SUVs as automakers are using uni-body construction instead of a full frame that attaches to the body.

Others buy SUVs for the dual-purpose capability. They may drive it like a car during the week, but also use it for weekend travel adventures which may involve pulling a boat, camper or motorcycles. Because they want their SUV to serve double-duty as a car and as a truck, they typically need a somewhat stiffer suspension that won't jar their kidneys, but can still handle the local scout troop and all of their camping gear.

Then there are those who actually buy SUVs to go off-roading. This may range from an occasional foray into the wilderness to a serious trek across boulder strewn terrain.

This type of SUV owner definitely needs four-wheel drive, tires that can deliver sure-footed traction on all types of terrain, and a suspension that can handle the rigors of the Rubicon or any really difficult off-road trail that quickly separates the weekend wannabies from those who know what they're doing.

Picking the Right Ride Control Product
Because SUVs may be used in so many different ways, it's difficult to design one ride control product that can satisfy every possible use - though some of the adjustable shocks come pretty close. Different types of driving styles typically require different types of valving and body construction.

For a smooth ride, a low pressure gas shock with relatively soft valving would be recommended. For extra control when towing or driving on rough terrain, a stiffer shock or a high pressure monotube shock would work well. If the suspension has been raised to increase ground clearance, shocks with longer travel would be required to keep the dampers from bottoming out.

Click To See the Shocking Truth About Ride Control

Ride Control & Safety
One thing the owners of many SUVs are especially concerned about these days is safety. Nobody wants to drive a vehicle that's potentially unsafe - and worn shocks can increase the risk of losing control in certain driving situations or an emergency. Safe driving requires shocks that are in good condition and engineered for the type of use the vehicle will see in everyday driving. Safe driving also requires tires that are in good condition, properly matched to the application (load rating, temperature, traction, etc.) and properly inflated for load and speed conditions.

It also requires a steering system and linkage that is not worn, wheels that are properly aligned, and brakes that can stop the same as when the vehicle was new.

A problem in any one of these areas can undermine the safety and increase the risk of losing control under extreme driving conditions or in an emergency. That's why the shocks, steering, tires and brakes on every SUV should be inspected at least once a year or every 12,000 miles by an ASE-certified technician. If repairs are needed, they should be done ASAP.

You can't always rely on the seat of your pants to tell you when the shocks are shot because a shock's dampening ability slowly declines as the miles add up. The loss of ride control is usually so gradual that most people don't notice how bad it's become until the shocks are long overdue for replacement.

What Shocks and Struts Do
The shock absorbers and struts are there to dampen spring oscillations. When a wheel hits a bump or a dip in the road, the suspension reacts by moving up or down (jounce and rebound). With no dampening, the wheel would continue to hop off the pavement and continue to bounce until friction in the suspension eventually brought it back into steady contact with the road. The result would be a very harsh and bouncy ride - and possibly loss of steering control on a rough washboard surface.

Shocks keep the suspension under control by creating a calibrated amount of resistance. Inside is a piston cavity (pressure tube) partially filled with hydraulic fluid. In the middle of this cavity is a two-way piston that's connected to the piston rod.

The up-and-down telescoping action of the shock or strut works the piston back and forth against the fluid in the cavity, creating hydraulic friction that resists and dampens the oscillations of the suspension. It's a simple yet effective technology that has worked well for many years.

The piston typically has a spring-loaded metering valve with orifices or a deflection disk that controls how much fluid bypasses the piston as it pumps up and down. In the bottom of the shock is a second metering valve that allows some of the fluid to circulate back and forth between the pressure cavity and the outer fluid reservoir cavity that surrounds the inner tube.

This is the "double wall" shock construction that is used for most original equipment and aftermarket replacement shocks. In "monotube" shocks, there is no outer tube and the hydraulic fluid is separated from a much higher pressure gas charge by a floating piston.

The calibration of the metering valves determines the dampening characteristics of the shock. The greater the resistance created by the metering valves, the stiffer the shock.

By staging the valving so the strut becomes progressively stiffer as it is extended further or pumped faster, a shock can be tuned to provide both a smooth ride and firm control when it's needed - which is just what an SUV needs.

Piston size is also a factor. The larger the bore size, the greater the volume of fluid that's displaced with every stroke, which provides greater dampening ability. Thus, heavy-duty shocks typically have larger bore diameters than standard shocks.

Shocks are also velocity sensitive, meaning the faster they're pumped, the more resistance they offer. All this churning creates a lot of heat, which must be dissipated to the surrounding air. On a rough road, a shock can get pretty hot. The rapid pumping can also aerate the oil and churn it into foam. Once air becomes mixed with oil, the oil no longer offers as much resistance and dampening ability begins to fade.

Enter gas charging. Gas-charged shock absorbers contain pressurized gas (usually nitrogen, but sometimes freon in a plastic cell) in addition to the hydraulic oil to minimize fluid aeration (cavitation or foaming).

The gas charge works like a pressure cooker to prevent the formation of bubbles in the fluid. This significantly improves ride control performance by reducing fade, noise and roughness. It also allows more latitude in shock valving, for a wider range of control.

One of the limitations of conventional fixed rate dampening is that the ride control characteristics of a shock are a compromise. This means a relatively firm shock that provides good stability on a smooth surface may be unacceptably harsh on a rough road or when hitting bumps. A soft shock that provides a velvet smooth ride and soaks up bumps, by comparison, may not have the resistance to limit body roll or nose dive under adverse driving conditions or sudden maneuvers.

Adjustable and Variable Valving
One way around this is to install replacement shocks that have adjustable valving so the damping characteristics can be changed to suite the type of driving that's being done. Shock manufacturers offer adjustable shocks that feature a wide range of adjustments. One brand of manually-adjustable shock features five settings that provide an 800% range in rebound and damping performance. A new line of shocks from the same manufacturer that offers 10 different settings will be available later this year. Plus, remote control packages can also be installed for changing damper settings on the go.

Adjustable shocks are available in gas-charged twin-tube and monotube designs for most SUVs including many of the new mini-SUVs such as Honda CRV, Toyota RAV4, Kia Sportage and others. Another way shock manufacturers improve ride control is to use some type of staged or variable valving. This allows the shock to self-adjust as the force and acceleration working on the piston changes.

One shock manufacturer, for example, uses a "velocity sensing" design with small grooves in the piston housing. The grooves allow fluid to bypass the piston when piston travel is in the midrange. This reduces the resistance for a smoother ride. When piston travel goes beyond the grooves, the shock becomes stiffer, providing a variable damping rate that can change as driving and road conditions change.

Another shock design that's on the road today is one that uses special "impact sensing" valving to deliver a relatively firm ride for stable handling, reduced body roll and nose dive without being overly harsh. Unlike velocity sensitive valving that creates more resistance when a shock experiences a hard bump, the impact sensing compression valving softens the blow by automatically opening a bypass that allows fluid to flow around the valve. This reduces the harshness of the impact and dissipates the jolt for a smoother, more stable ride. The driver also feels less steering feedback and harshness on rough roads as a result.

Impact sensing valving is designed to open within 12 milliseconds of an impact so fluid can bypass the piston when a hard bump is encountered. This occurs anytime an impact or acceleration of 1.5 G's is experienced to reduce the severity of the jolt. The valve then closes in 15 milliseconds to change the shock's damping characteristics back to normal.

The impact sensing shocks also contain a gas charge of 150 psi, which is quite a bit higher than a standard gas shock, to reduce fluid aeration and heat fade.

According to tests conducted by the manufacturer of this impact sensing technology, body roll can be decreased up to 12% during a J-turn maneuver, and pitch (nose dive) up to 18% when braking hard. This type of product is ideal for SUVs because of their high center of gravity.

Got a Ride Control Problem or Question? Need Help Now?

We have partnered with JustAnswer! to offer online email advice from expert mechanics who can answer questions for an affordable fee. Answers come via email in an average of under 15 minutes, you can ask follow up questions, and you only pay if you like the answer.

Need More Information On Shock Absorbers, Struts or Ride Control? Try Google Search. Enter Keywords or a Phrase:

Be sure to visit our other websites:

AA1Car Automotive Diagnostic Help Center
Carley Automotive Software
OBD2HELP
Random-Misfire
ScanToolCompanion
ScanToolHelp
TROUBLE-CODES

SUV Ride Control: Shock Absorbers & Struts

More Suspension Articles:

Got a Ride Control Problem or Question? Need Help Now?