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Car suspension

technology Maturity 9-11 Next article →

A car suspension is a complex system of mechanical parts.

Suspension System (PSF)
Suspension System (PSF)

It consists of tires, tire air, springs, shock absorbers, and linkages. This system connects a vehicle to its wheels while allowing relative motion between them. The suspension must perform two difficult, competing tasks. It must maintain road holding and handling for safety. Simultaneously, it must provide high ride quality for passenger comfort. Tuning a suspension requires finding the perfect compromise between these two goals.

suspension
suspension

The suspension manages forces transmitted through the tires' contact patches. When a vehicle travels over uneven ground, the suspension absorbs the impact. This process protects the vehicle, its cargo, and its passengers from damage and wear. The system works by managing spring rates and damping. The spring rate is a measurement of how much force a spring exerts when its length changes. For example, a heavy truck requires a high spring rate to prevent the vehicle from collapsing under its load. Conversely, a luxury bus uses soft springs to isolate passengers from road vibrations.

Pneumatic spring
Pneumatic spring

Engineers also calculate the wheel rate to understand how the car actually responds. The wheel rate is the effective spring rate measured at the wheel rather than at the spring itself. In many designs, springs are mounted on pivoting control arms or swing arms. This setup often means the wheel rate is lower than the actual spring rate. This happens because the lever arm ratio affects both the force and the distance traveled. In some non-independent designs, like a straight axle, the wheel rate can change depending on whether the car is braking or cornering.

Automotive suspension comparison
Automotive suspension comparison

Suspension technology has evolved significantly over centuries. Early ox-drawn carts used iron chains to allow the platform to swing. By the 17th century, these were replaced by leather straps called thoroughbraces.

Stagecoach exhibit, National Postal Museum IMG 4368
Stagecoach exhibit, National Postal Museum IMG 4368

Around 1750, leaf springs began appearing on carriages like the Landau. Obadiah Elliott eventually patented a spring-suspension vehicle using steel leaf springs. In 1901, Henri Fournier used a damped suspension on his Mors Machine.

Henri Fournier on the Mors machine
Henri Fournier on the Mors machine

This allowed him to win the Paris-to-Berlin race on 20 June 1901. He finished in 11 hours, 46 minutes, and 10 seconds, beating his closest competitor by over 45 minutes.

Different types of springs have shaped automotive history. Leaf springs were the first modern suspension system and were used on the Ford Model T.

In 1906, the Brush Motor Company introduced coil springs in the Brush Runabout. Today, coil springs are the standard for most automobiles. Other variations include torsion bars, used by Leyland Motors in 1920, and the De Dion tube. The De Dion tube is a semi-independent system that uses a yoke to tie wheels together. This design helped protect early tires by reducing unsprung weight.

Modern vehicles often utilize independent suspension. This means each wheel can move up and down without affecting the others. The Lancia Lambda pioneered independent front suspension in 1922. By 1932, this became more common in mass-market cars. Today, most vehicles feature independent suspension on all four wheels.

Independent rear suspension AWD
Independent rear suspension AWD

Rear suspension design often depends on whether the car is front-wheel or rear-wheel drive. Rear-wheel drive cars face more constraints because the suspension must work around the drive components. One popular historical method was the Hotchkiss drive, which used longitudinal leaf springs to transmit torque to the frame.

Finally, suspension affects how a vehicle moves laterally through the roll rate. The roll rate is the torque required to roll the vehicle's sprung mass. It is influenced by the vehicle's mass, track width, center of gravity height, and tire pressure. While the roll rate does not change the total weight transfer, it does change the speed and percentage of that transfer. Understanding these complex interactions between spring, wheel, and roll rates allows engineers to build safer, more comfortable vehicles.

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🖼️ Images & Media (11)
File:Suspension System (PSF).png
Suspension System (PSF).png
File:suspension.jpg
suspension.jpg
File:In Car Micheal Fitzgerald Cork Racing.jpg
In Car Micheal Fitzgerald Cork Racing.jpg
File:Stagecoach exhibit, National Postal Museum IMG 4368.JPG
Stagecoach exhibit, National Postal...
File:'24 Ford Model T (Auto classique Ste-Rose '11).JPG
'24 Ford Model T (Auto classique Ste-Rose '11).JPG
File:Henri Fournier on the Mors machine.jpg
Henri Fournier on the Mors machine.jpg
Citroën BX - Suspension - Maximum to minimum.ogg
File:Pneumatic spring.JPG
Pneumatic spring.JPG
File:Automotive suspension comparison.svg
Automotive suspension comparison.svg
File:Independent rear suspension AWD.jpg
Independent rear suspension AWD.jpg
File:M3Grant.jpg
M3Grant.jpg
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