Shock Absorbers

Cars and trucks have had shock absorbers for over 100 years. However, there are many types, and how they perform varies. In this article we’ll provide a little history, some info on shock absorber design, and provide some thoughts on what to choose for your car or truck. Let’s get started.

History

Before internal combustion engines, wagons often had leaf springs. The leaves in leaf springs rub against each other when a wheel goes up and down. That friction is a form of shock absorption, and is the earliest version of a damper in a wheeled vehicle.

Some early wagons had separate dampers, but they were primarily designed to limit the amount the wheel fell into a hole or change in road surface. In today’s terms they would be described as providing rebound only damping.

However, as cars got engines, vehicles moved faster and something more was required. Early shocks used a variety of materials: springs, rubber, and leather were some. The first hydraulic shocks were in use as early as 1901 but produced in volume starting in 1912. One of the earliest uses of hydraulic dampers were in Ford passenger cars in the late 20s.

Lever shocks were used by many manufacturers for decades to come, and British Leyland used them as recently as in the mid 1970s in MGs and Triumph sports cars.

Shock absorbers in modern vehicles

The tubular shock absorbers we’re all familiar with also emerged in the early 1900s, but didn’t come into common use until the 1930s. At that time there were two basic types of shocks:

  • Twin tube, consisting of two nested tubes and a compression, or base valve. When the piston moves when the car goes over bumps, hydraulic fluid moves through orifices to different chambers. This absorbs the suspension movement energy, dissipated as heat. Twin tube shocks can be hydraulic or gas charged.
  • Mono-tube, which has only one tube but two pistons, one working one floating. Both work together in response to suspension movement, and also dissipate the suspension movement energy as heat. Mono-tube shocks operate with high gas pressure, usually nitrogen.

Although there are many manufacturers of both types of shocks, Koni was a pioneer in twin tube hydraulics, and Bilstein was an early producer of mono-tube high pressure gas. Both companies still produce those dampers. Of the types of shocks available, hydraulic shocks with low pressure gas are probably the most common.

There’s more

As the automotive industry grew, other technologies emerged. The most common are forms of adaptive suspensions. This technology was pioneered by Citroen, who used hydraulic fluid and compressed gas to provide both springing and damping for their vehicles. More modern suspensions have solenoids and valves that control damping characteristics for hydraulic and gas shocks.

More recently, GM pioneered MagneRide which uses electrical pulses and fluid with metallic particles to offer changes to damping in response to road conditions.

Finally, air springs have been around for a very long time, but gained popularity when combined with pumps in (mostly) luxury vehicles to provide variable ride height and damping.

Enough history. What does this all mean to you, when you’re shopping for new struts and shocks for your car? Let’s look at who makes what, and how they perform.

Replacement shocks: OE and Aftermarket

How do you decide what replacement shocks to buy for your car? It will probably depend on a few factors:

  • How much you like the stock dampers
  • Cost of OE versus aftermarket
  • A specific performance requirement, like autocross use or towing
  • What’s readily available for your vehicle or what your repair shop can get for you.

The aftermarket for shock absorbers is big and active. And some manufacturers sell both to OE and the aftermarket, like Monroe, Sachs, and KYB. Others, like Bilstein and Koni, have no or very limited presence in OE applications.

How do you choose? Here are some things to consider.

  • OE shock design: See if you can find out if your OE shocks are twin tube hydraulic or high pressure gas. You may want to pick new shocks that have the same design. If you can’t find out, odds are they are twin tube low pressure gas.
  • What’s popular for your car: Enthusiasts for some cars have a “favorite” brand replacement shock. For example, BMW and Ford truck owners seem to favor Bilsteins, although for different reasons. Volvo owners traditionally like Konis. And Mercedes owners often prefer OE Sachs replacements. Poke around on forums or car club sites and see what people like for your car, and why.
  • Fitment: Aftermarket shock manufacturers often consolidate multiple OE part numbers into one shock absorber. If your car is an unusual model or trim level, the aftermarket dampers may perform differently on your car than other models.

For example, Koni specifies the same strut and shock set for a Volkswagen 2-door Golf as a Jetta Sportwagen, even though the Sportwagen is longer, some 300 lbs heavier and has different springs. The Konis aren’t going to ride or handle the same on both cars.

Cost, longevity, and warranty coverage are also factors. Many drivers like OE struts and shocks but feel they don’t last as long as aftermarket units. And as replacement labor costs rise, buying products that will last longer may save money, even if they’re more expensive at the outset.

Finally, the owners’ ride and handling preferences are highly subjective. While some may find a Bilstein HD to be a  smooth riding shock, others may find them overly harsh. Conversely, some drivers may like Koni Special Actives for their compliant ride, others may find they aren’t responsive enough when cornering.

What else do you need

A final thought: Don’t shortcut the installation bits and hardware. Some vehicles may only require new mounts (Volkswagens, for example) and new single use install bolts. Others, like BMW, have spring buffers, etc. that are rubber, and therefore wear items. If you install new dampers with old mounting parts the result will probably be less than what you were hoping for.

A little research, some shopping around, and, we hope, some of the information we’ve provided here will help you make a good choice when updating suspension. Diesel on!

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