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The "Shocking" Truth

By

Dennis R. Franklin
Franklin's Tire and Suspension
Yuma, AZ

Let's take a  look at another mystery, shocks and struts. Just like anything else, if you donít understand it you are prone to make a mistake. Shocks are no exception. There are so many misnomers in the market place that most shops who sell shocks and struts have only a general idea what they do and how they work. They do know this though, if they can talk you into a set of shocks they make money. My goal here is to give you the information you need to make the proper decision.

The name Ďshock" is really misleading. The proper name should be "spring damper". You see a shock doesnít absorb shock at all it controls the spring. Its job is to try and maintain the vehicles ride height at all times. (Thatís how high your car sits) A suspension system and its associated alignment angles are dependent on this. When we look at a car, we see it standing still. But the truth is it is used in a dynamic state, moving. The shocks job is to control the spring so the suspension operates as close as possible at the correct ride height. Letís look at a spring for a second. A spring may be supporting lets say 1200 lbs. Static or not moving. You then hit a dip in the road. The weight of the car upon hitting the dip compresses the spring to the point itís pushing back with 3500 lbs. of force. With out something to control the rebound the car would be lunched into outer space when the spring unloads. A shock then controls how much compression will take place, how fast it will compress and just the opposite when the spring unloads. Thereís a tremendous amount of energy being generated and controlled during this process. The shock is really an energy converter. It takes motion and converts it to heat. Whether itís just the seams in the road or a big dip in the road this process or "cycle" occurs at the rate of about 1150 times a mile. Or 34.5 million times in 30,000 miles. Can a shock wear out? What do you think? 

The Relationship Between Shocks and Tire Wear

Yes, there is a direct connection. The next time you go outside to get into your car, look at the contact point between the tire and the road. . You will note that the weight of the car is flattening out the tire creating a contact patch. When youíre moving down the road things change. If you hit a little dip in the road the suspension will compress, squashing the tires down with almost twice the load they had when at rest. They are in a sense, under inflated for the load theyíre carrying. If the shocks are weak, the springs all wound up and full of energy, rebound pushing the weight of the car off the tires. The tires now become over-inflated. Tires tend to wear on the outside when under inflated and in the center when over inflated. Ether one will cause premature tire wear. But thereís more. Lets look at a little thing called load shift. You drive your car into a turn. The load isnít even on all four tires anymore; it transfers to the outside tires. This means that the tires in the inside of the turn are now over-inflated and the outside ones are under-inflated. When you stop your car a similar thing occurs. The load transfers to the front of the vehicle. You guessed it, the front tires are under-inflated the rears are over-inflated. The real abuse occurs when braking takes place in a turn. Itís not uncommon for the outer third of the outside front tire to carry over half the weight of a car as it transitions through a turn. Shocks are designed to limit how fast and how much of a load will transfer in a dynamic situation. If you add to this equation suspension alignment change, this has a tremendous effect on tire wear. I understand this is probably a lot more then you ever wanted to know about what shocks do but itís the only way I know of explaining the importance of them.

The changing times can be shocking

Letís face it, we live in changing times. Years ago almost all cars had shocks. Then a thing called "struts" entered the market. Struts, unlike shocksí have two jobs to do. As well as the damping function, struts are the main structural part of the suspension. Manufactures went to this design because of weight and cost. Thatís the simplified version. The point is they are part of the brake system, steering system and wheel alignment. They are in essence "the suspension". Doesn't this sound expensive? Well your right, it is. To replace a shock, expect to pay $8-10.00 in labor plus about $20.00 dollars a shock. or 4 for $120.00 (for a lightweight car) The average to replace a strut is about $40.00 labor and $55.00 a strut. For four (if your car were equipped with 4 struts) you would pay $340.00. Any time a structural component of a suspension is changed the alignment must be checked. That means up to $390.00 to change the ride control. Remember this is an average price, if the vehicle has rear air struts you can easily add $200.00, if it has electronically controlled units the total can reach $900.00. Quite a chunk of change but not as bad as you think. On the older cars you ended up changing shocks about every 25,000 to 45,000 miles. If you did you would have spent about $240 dollars. Add to that the fact that strut type suspensions replaced over half the moving parts of a conventional system there is very little to wear out and replace. Bottom line, over all strut type suspensions save the consumer money in over all vehicle maintenance costs.

TRUCK SHOCKS

Shocks for trucks have a big job to do when you consider all the factors. This is quite a vague statement but vehicle heights, weight, spring rates, unsprung weight, type of tire and the intended use of the vehicle, are the basic factors. Design engineers have to work with normal parameters like 2 people in a pickup with moderate to no loads (look around at how many trucks are empty and with only the driver) take in to account these "factors" and still provide a smooth ride. They also have the task of making one shock fit as many vehicles as possible. For example, an extra heavy shock for a Chevy Van is the same for a Ĺ ton 6 cylinder up to a 6.2 diesel 1 ton. If you havenít seen it yet, after market shocks for the most part are compromises. If you use your sport utility or pickup like a car you are OK, the standard stuff works. If your vehicle is; a work truck thatís loaded all the time, a motor home, a truck with a big camper on all the time, larger then stock tires and wheels, anything out of the normal, then a specialty shock may be what you need. Bottom line. Spend money on something that wonít work is just throwing your money away. Spend a little more and you end up with a lot more. Products like Bilstien, KYB and Rancho (made and owed by Monroe) just to name a few, design shocks for such applications. Rancho makes a very unique product called a 9000 or "5 speed" that is adjustable. Either from the cab or manually, these shocks can be adjusted to fit a wide range of uses. Set on 4 or 5 they can make a camper solid as a sports car down the high way, take the camper off set the fronts at 3 and the rears on 2 and you have a Cowboy Cadillac instead of a buck board. My advice is to not rush, take your time, and ask a lot of questions, read specialty magazines (trailer Life is a good one) before making a choice (these can cost up to $350.00 a set so donít rush). And above all, try to not let price be the deciding factor. Get the best price for the product that will do the job and youíll be very happy.

Remember that this report is provided as a free public service of this web-site. The author is not an employee of either provider and has no association with either. Information is considered to be accurate to the best of our knowledge. As of the above date the information is Copyrighted, the sole property of the author, and unauthorized reproduction is prohibited.

Drive safe,

Dennis R. Franklin

 

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This page was last updated on October 13, 2002