Many motorists don’t appreciate the importance of ride control and how it affects driving, handling and braking safety. Not replacing a worn set of shocks or struts may seriously compromise the ability of the vehicle to handle bumps, dips, crosswinds or extra weight. Worn shocks and struts also will increase wear and tear on other steering and suspension components, too.
On rough roads, worn dampers that fail to keep the wheels in firm contact with the road may increase stopping distances. Tests have shown that stopping distances increase significantly when the tires bounce and lose grip on the road. This also hurts traction when accelerating and cornering.
Shocks and struts should be replaced when they no longer provide adequate ride control or fail to meet the driver’s expectations. Replacement is also required if a shock or strut is leaking, broken or damaged.
The best way to evaluate the condition of a vehicle’s dampers is a test drive on a variety of road surfaces (smooth and rough) and under various driving conditions (stopping quickly, cornering and changing lanes). Excessive body roll, sway or rocking would tell you the dampers are not up to the task and need to be replaced. For parts stores, of course, this method is not really practical. However, the old “bounce test,” can be easily done right in the store’s parking lot. To do the bounce test, rock the suspension up and down several times, then release it to see how many times it rebounds. As a rule, good dampers should stop the chassis from rocking almost immediately. Worn ones may allow it to rebound several times.
A visual inspection can also identify shocks or struts that are failing or have failed. Oil on the outside of the housing means the piston rod seal is leaking. The shock may still be doing its job, but for how much longer is anybody’s guess.
Ride Control Upgrades
A more compelling reason to replace shocks and struts these days is to upgrade handling and ride control performance. This approach seems to work best with motorists who want to improve the way their vehicles rides or handles.
If a vehicle is used to pull a trailer, a ride-control upgrade may provide a more sure-footed track without wagging or whipping, better stability in cross winds and better handling on curvy roads.
Popular upgrades include high-pressure gas shocks and struts with firmer valving or adjustable valving, shorter, stiffer springs to lower the center of gravity, stiffer sway bars to keep the body flat, and firmer suspension bushings to reduce suspension compliance.
Though most late-model vehicles come factory equipped with gas-pressurized shocks or struts, many OEM dampers are valved more for ride comfort than ride control. Soft valving provides a nice boulevard ride, but the trade-off is reduced body control and more roll — exactly what you don’t want on a vehicle with a high center of gravity like your typical SUV.
Gas shocks come in one of two basic varieties: single tube (monotube) and double (twin tube). The single tube variety has all its major components contained within a single large tube (thus the name) and typically uses a very high-pressure charge (280 to 360 psi). The gas charge is separated from the hydraulic fluid by means of a floating piston in the top or bottom of the tube. This type of shock must be manufactured with a heavier gauge cylinder and a highly polished internal surface (some are Teflon-lined).
A less-expensive alternative for upgrading ride control performance is the double- or twin-tube gas shock. Available from many suppliers of single-tube shocks, the double-tube design is essentially a gas-pressurized conventional shock with lower pressure. Some are in the 70-130 psi range while others are 112 to 130 psi or higher.