Mercedes-Benz
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Like other types of suspension springs, a leaf spring compensates for the up and down movement of the wheels as they traverse uneven surfaces. It's little more than a curved piece of metal, often made up of several steel plates called leaves stacked atop one another. The assembly mounts to the chassis either transversely (across the width of the vehicle) or longitudinally (along the length) and is somewhat elastic, meaning it will flex under pressure to help support the vehicle.
Though once commonplace, leaf springs have fallen out of favor with automakers in the past 50 years, but you can still find them on certain commercial trucks.
Volvo
Leaf springs date back to ancient times and evolved over centuries to support chariots, carriages, and eventually automobiles. Despite Buick's introduction of a rear coil suspension in 1938, a great many vehicles in the mid-20th century featured a combination of suspension types — often coils in the front, traditional leaf springs in the rear. It stayed this way until some time in the 1970s, when other suspension designs gained in popularity.
A number of heavy-duty trucks and commercial vehicles continue to use leaf springs, thanks to their affordability, reliability, and ruggedness. They're available as a weight-saving option on the Mercedes Sprinter van, for instance.
You can also find one on Volvo's largest crossover, although not for much longer. The Swedish brand will soon replace the XC90 SUV and its transverse-mounted leaf spring with the electric EX90, which will feature a multilink rear suspension.
This old-fashioned form of engineering graced Chevrolet Corvettes for generations, including the 2014-2019 C7. Even Chevy, however, dropped leaf springs in favor of coils with the debut of the mid-engine C8 in 2020.
There are a couple of reasons why leaf springs have fallen out of favor since their heyday. Namely, coil springs bend and flex more easily than leaves, providing a wider range of suspension movement. This gives automakers more options when it comes to tuning. They can install a stiff coil to maximize performance or a pliable one to maximize ride comfort.
Ram
Over time, leaf springs can lose their elasticity and flatten out. Without a bend, they can't absorb road irregularities and stabilize the chassis as intended. This will likely affect ride comfort and may even impair the responsiveness or handling of the vehicle.
If you have a vehicle with a worn-out leaf spring, you have some options. Aftermarket companies produce replacement leaf spring assemblies and in some cases entire coil conversion kits for all kinds of vehicles.