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Roadside Jerry
Roadside Jerry, Auto Mechanic
Category: Car
Satisfied Customers: 2948
Experience:  Auto Mehanic 39 years,30 with the NYPD Fleet Service Division
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University: worn shocks and struts on braking efficiency (as it

Resolved Question:

Can you cite the University of Cologne study about the effect of worn shocks and struts on braking efficiency (as it relates to braking distance)?
Submitted: 9 years ago.
Category: Car
Expert:  Roadside Jerry replied 9 years ago.

HelloCustomerI did find reference to the study in an article on worn shocks and struts. It states the study found one worn shock can increase the stopping distance by as much as four feet.I will send the article that mentions the study,I hope this will be what you need,if so please accept may answer,thanks and have a great day,Jerry.

Shocks and struts do far more than give you a comfortable ride. They affect your car's stopping distance and ultimately your safety. They also play a significant role in tire wear and steering control. Yet they are the most overlooked maintenance item in car repair today. Why? Because they're expensive to replace and most drivers aren't aware of their importance in safety and steering control.

What shocks do

We've all seen cartoons with characters on Pogo sticks. Now imagine your car with a Pogo stick at each wheel. You drive down the road and your tires hit bumps or potholes. At each bump, the spring compresses and then rebounds, sending the corner of your car soaring upwards. Launching that kind of weight upwards literally lifts the tire off the pavement, as well as shaking the fillings right out of your teeth. Worse than the initial rebound however, are the follow-up rebounds. Because as soon as the car reaches the peak of its first rebound, it begins its descent back onto the spring, compressing it a second time. This cycle of spring compression and rebound continues until the energy of the bump is dissipated. This is known as spring oscillation.


So the first job of a shock is to dampen or eliminate spring oscillation. Constructed just like a doctor's syringe, shock absorbers incorporate a plunger, a cylinder, and a non-compressible liquid. The bottom of the shock absorber contains the fluid filled cylinder and is attached to the lower control arm of your car, forcing it to take the first hit from the bump. The top end of the shock absorber is the plunger and is attached to the body of your car. As the plunger gets pushed in, it forces fluid out of the cylinder through a small valve, limiting the rate of compression of the spring. When the spring begins its rebound, the plunger sucks the fluid back into the cylinder. The valve in the shock allows the fluid to flow out of the cylinder faster than it can get sucked back in. That's how a shock absorber works to control spring oscillation, or rebound

Over thousands of miles, the seals around the piston and the valve itself begin to wear. Worn piston seals allow fluid to bypass the small opening in the valve. Instead, the fluid actually flows around the piston, provides far less resistance to spring compression. A worn valve allows too much spring compression and allows spring rebound to occur too quickly. The result? Spring oscillations.

The botXXXXX XXXXXne is that it's the shock's job to eliminate tire and car bounce and keep your tires firmly in contact with the pavement. A tire that's bouncing can't stop your car quickly. Even on flat pavement, an aggressive stop tends to lift the tire and cause bounce. Worn shocks increase that tendency. In fact, a University of Cologne study has shown that a single worn shock can increase your stopping distance by as much as 4 feet! That can mean the difference between life and death. A worn shock also affects steering control simply because the tire spends less time in contact with the road. Ever drive down a bumpy road and feel like your car wants to change lanes? That's the symptom of a worn shock.

Customer: replied 9 years ago.

Thanks for your reply. I am in the tire and repair business, so I understand the effect shock and struts have on vehicle suspension dynamics.

I would like to incorporate the findings of the Cologne study into conversations with my customers, but some are skeptical without solid "proof" of a claim. Customer perception of our business not good to begin with, so I want to insure the information I give my clients is trustworthy, reliable and verifiable. That is why my request for information centers around the ability find and archive the U. of Cologne research in order to "back up" a claim of increased braking distance due to worn out shocks or struts.

I apologize if my request was not clear. The information I am looking for is to find the research paper and have it available for customer viewing. If it is anything like the academic research I've seen, it may not make sense to an average consumer, but just offering the "proof" is enough to assure most drivers that the recommendation I make to replace suspension control derives from sound academic investigation supported by statistical rigor.

I look forward to your reply.

Kelly Craven (Customer)
Expert:  Roadside Jerry replied 9 years ago.
Hello Kelly, I found reference to the study, but not the actual paper. I would believe the only way to get a copy would be to contact the university itself ,sorry I couldn't be of more help,good luck with your search,Jerry.
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