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Ford OEM Parts - Shock Factor - Tech

Posted in Features on February 1, 2006 Comment (0)
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Several years ago, while conducting the vehicle evaluations for another publication, we were shocked (no pun intended) to discover that we had blown out the OEM shocks on a brand-new Ford we were testing.

This wasn't an uncommon occurrence for the off-road guys, who typically auditioned trucks and vehicles like they were racing Baja 1000. But for a truck driven solely on the street for our test, this was highly uncommon - or so we thought. No doubt we drove the truck hard, with cornering tests and several passes up and down a very steep and windy stretch of highway well known for motor vehicle testing.

Actually, with just over three full days of driving, we wore out the tires and brakes on all the vehicles, and had shock failure on two. Generally speaking, OEM shocks are built to last longer than most of the aftermarket shocks out there. This may sound surprising, however, consider that shocks are covered under standard manufacturer warranty and you'll understand why they're made to last.

Like tires, the aftermarket of shocks is literally flooded with junk. Parts with a "Lifetime Warranty" that will last between 10k and 20k miles (how's that for a shock?) are unfortunately common enough. Eighty-nine dollars for a solid, high-performance shock doesn't sound too bad until you times that by four and tack on an additional $50 per corner (on average) for installation if you don't bolt them on yourself. So a good majority of enthusiasts trim their budget and buy low-quality shocks. What they don't realize is that even with a lifetime warranty, it will cost them a couple hundred bucks to replace them sooner than expected. Sadly, most people only spend extra money on parts they can see - note the abundance of pristine, never-see-dirt, pre-runner and monster-style trucks now commuting on the freeways.

The bottom line is that shocks are arguably the most important safety feature on your vehicle - they keep the rubber on the road. This may not seem as important to the rigs that are taken to their destination on a flatbed and only see trail time, but the majority of four-wheelers today actually drive to their destination. This means that traction on the highway is just as important as it is off the highway.

In general, shocks are broken down into two basic categories: twin and mono-tube. And of course there is the adaptation of the mono-tube in the McPherson strut. Realistically, we don't use twin-tube shocks on off-road vehicles, so for the purpose of this feature we focus on the mono-tube and the various types of mono-tubes, hydraulic, gas-charged, and air piston.

Mono-tube shocks are higher-performance shocks as they are made to tighter tolerances. They have less variance and are best for off-road and racing applications as they dissipate heat faster. On the down side, they cannot be used in all applications such as struts. They allow a larger bore size to be used in the same space which gives you more damping control.

Generally speaking, hydraulic-type shocks are not practical for the rigors of today's off-highway driving. Hydraulic shocks, like gas-charged shocks, use a piston and special valving to dampen energy. Because the fluid cannot be compressed, it dissipates this energy by passing through the valves. Excessive movement actually results in the fluid starting to bubble which further hinders performance. To rebound, it must pass back through the valves. This recovery time relates to poor performance, thus making them impractical.

Gas-charged shocks, struts, and air-piston designs have much more advanced valving and result in faster reaction time - keeping your tires where they were meant to be. Simply stated, shock absorbers convert the kinetic energy of the spring movements into heat. This heat is then dissipated through the shock tube. Hydraulic fluid or oil actually holds heat longer versus gas or air which helps to dissipate heat, thus the faster the response time.

We sat down with Shane Casad who works in product development for ThyssenKrupp Bilstein of America to gain some perspective on what goes into the research and development of a new product.

4WD&SU: What are some of the key factors you consider when developing a shock absorber?

Shane: The major factor is building the shock to accommodate the application to improve the overall performance, ride, and handling.

4WD&SU: Explain the process in developing a new shock absorber.

Shane: Answering this question depends on what type of shock we are trying to build, as well as the desired performance increase. In this case, I can only assume you are referring to an application for a street legal off-road vehicle. Here is the process: When we build an application, we go through a process we refer to as "ride work." Basically, a vehicle is brought into our shop in San Diego, California. We determine the goals of the application and decide on which damper will be required. We measure for dimensions, in many cases optimizing travel. Once the prototype shocks are mounted, the vehicle is then driven on a set test track consisting of surface streets, windy roads, freeways, and rough dirt roads. During this time, the shocks will be taken off the vehicle and revalved until the desired goals are realized (during the revalve or "shock-tuning" phase, the damping rates are adjusted on the piston head for rebound and compression). On a Jeep or truck application, this process usually takes two to three days.

4WD&SU: Bilstein is well known in both on-road and off-road racing markets. Are there two separate engineering teams that address each market?

Shane: For Bilstein of America, there is one engineering team that addresses both motorsports and street applications. However, we have different Tech Groups that actually apply the products to the various markets. Our main specialties here are off-road racing, circle track, OEM, and aftermarket street performance. In Germany, there is a specialty motorsports group that works autonomously on the aftermarket and OEM groups; however, the only off-road vehicles they are involved with are World Rally cars

4WD&SU: Explain the process in developing a new shock absorber.

Shane: Answering this question depends on what type of shock we are trying to build, as well as the desired performance increase. In this case, I can only assume you are referring to an application for a street legal off-road vehicle. Here is the process: When we build an application, we go through a process we refer to as "ride work." Basically, a vehicle is brought into our shop in San Diego, California. We determine the goals of the application and decide on which damper will be required. We measure for dimensions, in many cases optimizing travel. Once the prototype shocks are mounted, the vehicle is then driven on a set test track consisting of surface streets, windy roads, freeways, and rough dirt roads. During this time, the shocks will be taken off the vehicle and revalved until the desired goals are realized (during the revalve or "shock-tuning" phase, the damping rates are adjusted on the piston head for rebound and compression). On a Jeep or truck application, this process usually takes two to three days.

4WD&SU: Bilstein is well known in both on-road and off-road racing markets. Are there two separate engineering teams that address each market?

Shane: For Bilstein of America, there is one engineering team that addresses both motorsports and street applications. However, we have different Tech Groups that actually apply the products to the various markets. Our main specialties here are off-road racing, circle track, OEM, and aftermarket street performance. In Germany, there is a specialty motorsports group that works autonomously on the aftermarket and OEM groups; however, the only off-road vehicles they are involved with are World Rally cars.

4WD&SU: How do Bilstein shock absorbers differ from competitors?

Shane: Bilstein was the first company to develop a mono-tube, high-pressure gas shock. This was a monumental achievement which changed the shock absorber forever. Bilstein produced its first mono-tube shock absorber in 1957 as an OEM supplier for Mercedes-Benz. Mono-tube shock absorbers were clearly more advanced then their hydraulic twin-tube counterparts.

In the '60s, Bilstein began to use shocks on motorsports applications and enjoyed a rich history of achievement. One particular event was the Baja 1000. Bilstein was the first company to create a specific off-road racing shock in 1972. This action produced unparalleled success in the off-road racing market, being the only shock of choice well into the '90s.

How does Bilstein differ from the competitors? In today's markets, many newer companies are building mono-tube shocks; however, with Bilstein you are buying a proven performer. Bilstein aftermarket performance shocks are derived from the actual components used on motor sports shocks. Basically, you are receiving custom racing shocks that will directly bolt on your vehicle at a reasonable price.

4WD&SU: Some companies offer air or liquid-piston shock absorbers - what is the advantage or disadvantage to offering gas-charged?

Shane: Mono-tube gas shocks are an advantage due to the ability to eliminate oil cavitations and shock fade. The heart of this system is what is called a "dividing piston." This separates the nitrogen gas from the oil while pressurizing the oil. This eliminates any inconsistencies in valving due to oil cavitation.

4WD&SU: How important is customer feedback to the engineering team?

Shane: Very important. Many of Bilstein's employees are big-time off-road enthusiasts, so we have a real good idea of what this market wants and needs. When ride work is complete for an application, we follow up with the customer for feedback.

4WD&SU: How has the market for shock absorbers changed over the past several years?

Shane: It is becoming more accepted to spend more money on shocks. This has greatly improved development due to the fact that better shocks usually are more expensive to build. This allows us to improve the product over time.

4WD&SU: What would you like those people who are in the market for shock absorbers to know before they buy?

Shane: How they intend to use the vehicle - street, off-road, racing, mud bogging, rockcrawling, monster truck racing, etc.

4WD&SU: What do you think (generally) of factory shock absorbers offered on today's SUVs and "off-road" vehicles from the dealership?

Shane: As long as they are Bilsteins, they are great! Many OEM truck and SUV manufacturers, such as GM, Dodge, Toyota, Nissan, Ford, Mercedes, and BMW, include Bilstein on their high-end off-road packages.

4WD&SU: How active is Bilstein in the off-road market?

Shane: We are very much involved. As I indicated before, someone from Bilstein is doing some type of off-road activity every weekend. As a company, we use off-road racing to showcase our high-end shocks. These activities provide an excellent platform to improve the Bilstein product. Case in point, have you seen the new Bilstein Blackhawk?

4WD&SU: What advice can you give our readers on shopping for shock absorbers? How can they "kick the tires" on models before they buy? And what should they look for and/or lookout for?

Shane: I would say forget about "perceived performance" and buy a shock that will best suit your needs. Bilstein has one of the widest off-road shock lines in existence. We offer fitments for trophy trucks to street trucks. Why? To have something for everybody! Given this selection, off-roaders can identify their activity (racing, mud bogging, rockcrawling, trail riding, monster truck freestyle, etc.) and have a Bilstein product which will perform for the job.

How to Tell if Shocks and Struts Need ReplacementUnder normal conditions, shocks and struts wear out gradually; however, many factors can affect how much wear is actually occurring and at what rate it is occurring. It's safe to say that two identical vehicles will have different driving habits, and those who take their vehicles off-road are more likely to wear out their shocks than the owner who doesn't. Worn shocks and struts not only affect the ride comfort and control of your vehicle, but can affect its braking effectiveness too. If your shocks are worn out and you brake hard, the front of the vehicle will dip - this extra inertia can result in added braking distances.

Here is a good self-test to check for signs of worn shocks or struts:* Do you experience excessive bounce (three or more bounces) when crossing an intersection or dip?

* When stopping quickly, does your vehicle rock back and forth several times?

* While applying your brakes firmly at higher speeds, does your vehicle have a tendency to drift left or right?

* When changing lanes quickly does your vehicle rock or sway from side to side?

* On a tight curve, like a freeway ramp, does your vehicle lean and sway giving it an uneasy and disconnected feeling?

Now obviously your truck handles differently now that it is setup for off-road use. This is why it's even more important to have high-performance gas-charged or air-piston shocks. While many variables contribute to the handling characteristics of your vehicle, inspection of your shocks or struts is an easy way to ensure your safety and comfort on- and off-road.

When inspecting your shocks look for the following:* A badly leaking shock or strut (hydraulic). The unit is losing fluid and can't provide the resistance it was originally designed for.

* Shiny spots at the contact point of the safety bumper, and marks between the coils of the spring called "coil clash." They are the result of topping and bottoming caused by excessive suspension travel.

In closing, choosing the right type of shock or strut for your off-road vehicle will greatly enhance your driving experience. Understand that companies such as Bilstein, Rancho, Tokico, and others spend hundreds of hours designing a shock that is built for your vehicle to deliver the driving experience you are looking for. Take advantage of their research and make an investment into your rig that is meant to last on and off the trail.

Sources

BILSTEIN OF AMERICA
Poway, CA 92064,

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