Q: What is an adjustable suspension, and how does it work?

asked by on August 25, 2016

What is an adjustable suspension, and how does it work?

Car adjustable suspension could mean two things, either adjusting the ride height of the car or changing the handling characteristics. Ride height systems are usually added to the rear of vehicles to raise the rear of the car and bring it back to level if it’s heavily loaded. Handling and braking can be adversely affected if the rear of the car is lower than the front, so it’s clear how this system is useful. Height control systems may be at all four corners, usually installed on high-end SUVs. In addition to compensating for different loads, four-corner systems can raise the vehicle for additional ground clearance, which is good for off-roading over rough terrain. Why not just make the higher ride height permanent? The higher center of gravity with the vehicle raised is not optimal for going around corners at higher speeds on smooth pavement, so the adjustable ride height is less of a compromise.

Adjusting the ride height can be accomplished in a number of ways. The least complicated is integrating air bags into the rear shocks and having a small vehicle-mounted compressor raise the air pressure when more height is needed. Some systems replace the coil suspension springs with air bags, again adjusting the air pressure to change the level of the car. The most involved are hydraulic systems where oil is pumped at high pressure into a suspension member, usually a main part called a strut, which changes the ride height. Rear “leverer” systems are usually automatic, using a sensor to detect if the car is low or high; four corner systems are driver selectable.

The second system can alter the handling characteristics of the vehicle by changing how the shocks respond to road inputs. Stiffer shocks give a more responsive feel when you want the car to change direction, but the compromise is a harder ride quality. Adjustable shocks are a way to get around this. In its most basic, a shock is simply a tube filled with oil with a piston moving up and down the inside of the tube. The amount of damping is set by valves in the piston that control the rate that the oil flows past the piston. Letting less oil through means stiffer shocks, while letting more oil go through means less damping and a softer ride.

Shock adjustment methods vary widely, from something as simple as a knob or screw on the shock itself for manual adjustment, to very advanced systems with sensors that that feed vehicle speed, yaw rate, steering wheel angle, rate that the steering wheel is turned, and body vertical travel and rate into an ECU that outputs a signal to each individual shock, electronically adjusting the valving according to driving conditions. Typically, the electronically controlled systems have a cockpit switch allowing the driver to select different settings, such as sport or comfort.

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