What does a Car's Suspension System do?

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  • Written By: R. Kayne
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The very important job of a suspension system is to smooth out the ride while maintaining excellent control. This may sound like a simple job, but with acceleration comes force, and force translates into raw energy. The system is made up of several parts that can vary depending on the type of suspension, but typically include the chassis or frame, coil springs, leaf springs, dampeners including struts and shock absorbers, and anti-sway or torsion bars. Various combinations of these might form a particular system.

When a vehicle accelerates down a road, bumps cause forward energy to be converted into vertical energy, which travels through the frame of the vehicle. Without coil and leaf springs to absorb this, the vertical energy would cause the vehicle to jump up off the road, reducing tire friction and control. The car would then come bounding back down with even greater force, making for a very uncomfortable and dangerous ride.


Coil springs and leaf springs are designed to absorb up/down forces to keep tires firmly planted on the ground. Passenger cars commonly have coil springs in front and leaf springs in the rear, while many 4-wheel drive utility vehicles, sports utility vehicles, and trucks have coil springs in the front and rear, or independent front/rear suspension. Dampeners, namely struts and shock absorbers, dissipate the energy absorbed by coil springs, so up/down motion is quickly quieted to zero. If the dampeners are in proper working order, the passenger cabin should remain fairly unaffected by traveling over dips or bumps in the road. When shock absorbers are old or faulty, once the car starts bouncing, it continues bouncing for elongated periods of time.

Some vehicles benefit from torsion bars, also called anti-sway or anti-roll bars. These bars span the frame, helping to level out side-to-side motions while cornering. Torsion bars are an important feature on high profile vehicles that are considered top-heavy.

While passenger and luxury vehicles have systems designed for maximum comfort, stiff suspension systems are typical of utility vehicles designed for carrying heavy loads. Vehicles that have been lifted for a higher profile, often for off-roading, replace key parts of the system. Lift kits are designed for a particular model to compensate for the shift of weight and how it will affect the steering and suspension.

A vehicle that does not sit level or has excessive bouncing or poor handling is demonstrating problems associated with the suspension system. This greatly affects the vehicle's safety, so it should be repaired before driving.


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Post 4

Could a bad coil spring cause a leaf spring to fail?

Post 3

@Parmnparsley- Beyond physical damage, deciding when to change shocks and struts is completely subjective. If the housing is damaged or bent than the shocks should be changed. If the shocks are leaking fluid, than it is time to change them. These are often the only reasons that a warranty will cover shocks unless the car is obviously bouncing or bottoming out.

Technically, a shock should be changed after 60,000 miles because they will gradually lose their dampening ability. Signs that your shocks are worn down would be excessive nosedive during braking, bouncing after a bump, or poor handling in moderate wind. Excessive rocking when other cars pass is also a sign of weak shocks or struts.

Post 2

I don't really know much about cars and I am wondering how to tell when my suspension parts are worn out. How do I know when it is time to replace my shocks and struts?

Post 1

I would just like to point out that cars are not all meant to sit level. Trucks and some SUVs have a higher ride height in the rear, making their suspension look nowhere close to level.

The lower profile in the form allows for a shorter turning radius, better road view, and better overall handling. The taller suspension in the rear is to enable a heavier payload capacity. Often people will add an extension to the front coilover suspension to correct this downward pitch.

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