Shock absorbers, springs and alignment.
01-15-2007, 09:11 AM
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Shock absorbers, springs and alignment.
Another suspension query from a layman.
I am currently readying my bank account to take a hit when I buy some Bilstein HDs, have them fitted and then have the alignment reset. The main reasons for doing this are that my car's front end feels "vague" once I build up some speed, and my original M030 shocks are now around 10 years old.
I have read much in this forum about the "night and day difference" people have experienced when they have had similar work done, but I wonder how much is down to the new shock absorbers, and how much is due to the re-alignment.
As I understand it, the shock absorber simply dampens the recoil in the spring, therebey reducing the number of bounces after it has be compressed.
If that is so, is most of the "night and day difference" that people report down to having their cars' suspension correctly aligned after its setup has gradually become degraded over the years?
As I said above, my car's steering does become vague at speed, but since this happens on smooth, flat, straight roads (and so the shock absorbers are pressumably "inactive"), isn't the cause misaligned suspension rather than worn shock absorbers?
TIA for any guidance/education received
I am currently readying my bank account to take a hit when I buy some Bilstein HDs, have them fitted and then have the alignment reset. The main reasons for doing this are that my car's front end feels "vague" once I build up some speed, and my original M030 shocks are now around 10 years old.
I have read much in this forum about the "night and day difference" people have experienced when they have had similar work done, but I wonder how much is down to the new shock absorbers, and how much is due to the re-alignment.
As I understand it, the shock absorber simply dampens the recoil in the spring, therebey reducing the number of bounces after it has be compressed.
If that is so, is most of the "night and day difference" that people report down to having their cars' suspension correctly aligned after its setup has gradually become degraded over the years?
As I said above, my car's steering does become vague at speed, but since this happens on smooth, flat, straight roads (and so the shock absorbers are pressumably "inactive"), isn't the cause misaligned suspension rather than worn shock absorbers?
TIA for any guidance/education received
01-15-2007, 09:46 AM
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Does it seem to wander, for lack of better words, as if your tires are finding rails in the road? If so, I would say alignment mostly. However, the shock also provides a stabilizing point for the spring-a hold point if you will. A completely blown shock, especially fronts, will make the car feel "loose" in the front because of the lack of consistent downforce to the suspension.
So, could be both.
So, could be both.
01-15-2007, 10:16 AM
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Properly functioning shocks are more about predictable response at all four corners and road contact, than anything else.
When the spring is deflected, it stores energy. Without shocks and struts the spring will extend and release this energy at an uncontrolled rate. The spring's inertia causes it to bounce and overextend itself. Then it re-compresses, but will again travel too far. The spring continues to bounce at its natural frequency until all of the energy originally put into the spring is used.
If the struts or shock absorbers are worn and the vehicle meets a bump in the road, the vehicle will bounce at the frequency of the suspension until the energy of the bump is used up. This may allow the tires to lose contact with the road.
Struts and shock absorbers that are in good condition will allow the suspension to oscillate through one or two diminishing cycles, limiting or damping excessive movement, and maintaining vertical loads placed upon the tires. This helps keep the tires in contact with the road.
By controlling spring and suspension movement, components such as tie rods will operate within their design range and, while the vehicle is in motion, dynamic wheel alignment will be maintained.
Therefore, with properly functioning shocks, you are able to maintain proper alignment even during suspension response. When coupled with a proper alignment, it produces the "night and day" difference that people experience.
However, the suspension system is just that--a system. If any one part of that system is not functioning properly, the whole system will be compromised.
So, what to do? You could try simply realigning your car to see if that's enough. However, considering the cost to properly align our cars and the fact that if you're wrong, you will need to realign the car after the shocks are installed, it is often desireable to do it all at once. Furthermore, with the known short life of the stock shocks, I'd put money on the fact that at least one of your shocks is shots.
When the spring is deflected, it stores energy. Without shocks and struts the spring will extend and release this energy at an uncontrolled rate. The spring's inertia causes it to bounce and overextend itself. Then it re-compresses, but will again travel too far. The spring continues to bounce at its natural frequency until all of the energy originally put into the spring is used.
If the struts or shock absorbers are worn and the vehicle meets a bump in the road, the vehicle will bounce at the frequency of the suspension until the energy of the bump is used up. This may allow the tires to lose contact with the road.
Struts and shock absorbers that are in good condition will allow the suspension to oscillate through one or two diminishing cycles, limiting or damping excessive movement, and maintaining vertical loads placed upon the tires. This helps keep the tires in contact with the road.
By controlling spring and suspension movement, components such as tie rods will operate within their design range and, while the vehicle is in motion, dynamic wheel alignment will be maintained.
Therefore, with properly functioning shocks, you are able to maintain proper alignment even during suspension response. When coupled with a proper alignment, it produces the "night and day" difference that people experience.
However, the suspension system is just that--a system. If any one part of that system is not functioning properly, the whole system will be compromised.
So, what to do? You could try simply realigning your car to see if that's enough. However, considering the cost to properly align our cars and the fact that if you're wrong, you will need to realign the car after the shocks are installed, it is often desireable to do it all at once. Furthermore, with the known short life of the stock shocks, I'd put money on the fact that at least one of your shocks is shots.
01-15-2007, 10:31 AM
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Thanks guys.
Jeff, a special thanks to you! As you did when I posted a few related questions a few weeks ago, you have provided a superb explanation.
Seems like my bank balance will need to take the hit. Having a number of other things I want to spend money on (on the car) I was wondering if (or perhaps more accurately, hoping that) I could get away with a GBP300 realignment instead of GBP1250 for shocks, fitting and realignment. Oh well, I guess the cosmetics will have to wait a while.
Thanks again.
Jeff, a special thanks to you! As you did when I posted a few related questions a few weeks ago, you have provided a superb explanation.
Seems like my bank balance will need to take the hit. Having a number of other things I want to spend money on (on the car) I was wondering if (or perhaps more accurately, hoping that) I could get away with a GBP300 realignment instead of GBP1250 for shocks, fitting and realignment. Oh well, I guess the cosmetics will have to wait a while.
Thanks again.