Unequal Rear Suspension Settings?

[xsport]

Another point is that if the shocks are not equal length when fully extended , then this will give a different ride height. I had this problem when i bought new shocks. The seller listed them as suitable for rover 75. They were in fact the mgzt rear shocks,which were shorter,as are the springs. Apparently , the last R75 used the mg set up on them, ( contempory models ) so ,if the shocks or springs are not the same each side , it will. Unless they were all renewed in pairs of the same,then you will have ride height differences. Even heavy duty springs (which i have fitted on the rear) sit much higher. When shorter shocks are fitted ,or shorter or stronger springs fitted, then they are already compressed lower than the originals. Simon has made a reply request,which i am interested in too ....

[Kearton]

Originally Posted by SD1too

I see that you are a professional engineer Ken so can you help me with this please?

Whenever I fit a shock absorber I have to raise the car body very high, beyond spring-determined height, in order to insert them. When the body is subsequently lowered the spring partially compresses but so does the shock absorber. A point of equilibrium appears to be reached. Surely this would depend upon the ability of both the spring and the pressurised shock absorber to compress, wouldn't it?

If I removed my shock absorbers completely, would you say that the car's body height would be identical to that with the spring/shock absorber combination fitted?

I'd be grateful if you could explain where I am going wrong with this.

Simon

Try a static damping test: Stand beside one corner of your car, push it down hard & then let go. When the spring pushes the body back up it overshoots the normal (rest) position then drops back to it. This is correct damping.

Explanation
When a car is sitting in its normal position (rest), the suspension must be partly compressed. (Typically by 1/3 of its travel as I understand it.) This is so that the body can move both down and up relative to rest when it goes over bumps.

A) If the damper were at its longest position when the car was at rest, when depressed it would go down, rebound to the rest position, then hit the top of the damper and break it.

B) If the damper were at its shortest position when the car was at rest, when you pushed down it would not move as it would be acting as a solid rod, giving a very uncomfortable ride.

An Aside
Drag racing cars often have rigid or very stiff dampers so that they don't compress when starting off so that the weight on the wheels, and hence the grip, is better.

I hope that helps.

[sworks]

It’s as simple as….
The springs are there to carry the weight of the vehicle and provide up and down movement of the suspension whilst keeping the vehicle level and to carry the weight of the vehicle. The ride height is regulated by the spring hence why you get ‘lowering’ springs. The damper is there to control and ‘dampen’ the operation of the Spring and in doing so keep the wheel on the road. The dampers are not weight carrying.
You can get lowered or shorter dampers but these aren’t to do with the height of the vehicle but the height of the spring, a lowered spring needs a shorter damper to control it effectively.

[xsport]

Yes agreed. But everything mentioned in the past posts will depend upon having the correct shocks and springs fitted , and that they are all functioning equally and correctly. We wont know this until this status has been confirmed from the original poster. Variants in springs and shocks will bring different ride qualities and properties ,but most importantly is that they are equal each side .Thanks sworks for the post. ...

[SD1too]

Yes, thanks Mark and Kearton.

This is the interesting bit.

Originally Posted by sworks

The dampers are not weight carrying.

I understand what you're saying Mark but if that was absolutely true wouldn't it be possible, with the car resting on its wheels, to undo the damper's fixings and just slide it out? But that's not possible.

As Kearton has said, the damper is partially compressed. It contains gas under pressure so doesn't that provide some support to the body, albeit much less than the spring?

Simon

[shiner]

Originally Posted by SD1too

Yes, thanks Mark and Kearton.



This is the interesting bit.



I understand what you're saying Mark but if that was absolutely true wouldn't it be possible, with the car resting on its wheels, to undo the damper's fixings and just slide it out? But that's not possible.



As Kearton has said, the damper is partially compressed. It contains gas under pressure so doesn't that provide some support to the body, albeit much less than the spring?



Simon

As mark stated Simon the weight of the car is held by the springs . The dampers are slightly compressed in location to allow for dampening effect.
View it another way . Springs hold the weight and absorb impacts.
The 'shock absorbers' and in fact just dampers to dampen the springs rebound.
All I / we can do is explain it to you , we can't make you understand it.

Sent from my 2201116SG using Tapatalk

[Mike Noc]

Originally Posted by SD1too

I understand what you're saying Mark but if that was absolutely true wouldn't it be possible, with the car resting on its wheels, to undo the damper's fixings and just slide it out? But that's not possible.

Simon

That's exactly what I did Simon, with the car on the ground unscrewed the bolt retaining the shock absorber to the hub and removed it. I had a suspension knock and wanted to eliminate the shock absorber so took it out of the equation.

Simples!

The only way shock absorbers can affect ride height (assuming the correct ones are fitted) is if they start to break up and debris blocks the internal channels the oil passes through. I've had this happen on my car where the NSR of the car got lower and lower as I drove because the shock absorber bound up until all the suspension movement was effectively used up. Left the car for half an hour and normal ride height was gradually resumed.





.

[dave lincs]

Originally Posted by SD1too

Yes, thanks Mark and Kearton.

This is the interesting bit.

I understand what you're saying Mark but if that was absolutely true wouldn't it be possible, with the car resting on its wheels, to undo the damper's fixings and just slide it out? But that's not possible.

As Kearton has said, the damper is partially compressed. It contains gas under pressure so doesn't that provide some support to the body, albeit much less than the spring?

Simon

As I said before it's quite Simple Simon try it on you car and let us know the results then we will have the evidence that you are usually so keen on

[Kearton]

Originally Posted by SD1too

Yes, thanks Mark and Kearton.
[SNIP]
As Kearton has said, the damper is partially compressed. It contains gas under pressure so doesn't that provide some support to the body, albeit much less than the spring?

Simon

Hi Simon, that is not the case. I'm sorry if my explanation wasn't clear.

At rest, the spring will be partly compressed and thus under load.
The damper too will be partly compressed, but will not contain any pressure.

A damper only contains pressure when it is moving. Its job is to slow down movement. It does this by restricting/slowing the flow of a fluid between its two chambers. Once that flow has been completed, there is no pressure. If the flow is blocked for any reason, the damper will behave like a solid rod.

IHTH

[SD1too]

Thank you Kearton. That's helpful.

Simon