erez wrote:ok, the car is 2.0 8V 1997 without hydractive, hatchback
Ok in that case the rear spheres should be 30 bars.
HOW HIGHER PRESSURE CAUSES SOFTER RIDE?
(i'm shocked)
Well, without launching into a whole lot of maths, here is the simple explanation.
The quoted gas pressure of a sphere is its "pre-charge" pressure, which is the pressure when the sphere is not used, for example not fitted to the car.
When the hydraulic system pressurizes to lift the car the hydraulic pressure will rise to that necessary to lift the weight of the car, and in doing so it will compress the pocket of gas trapped by the sphere diaphram to the same "operating" pressure as the oil.
This means the gas pressure under actual operation is the same regardless of how much gas is in the sphere, it is determined only by load weight. However the compressed *volume* of gas in the sphere will depend on the pre-charge pressure.
High pre-charge pressure means not much compression of the gas required = larger volume, low pre-charge pressure means a lot of compression of the gas required = smaller volume.
Springing constant is defined as change in force over change in length. On a hydraulic system this translates to change in pressure for a given cubic displacement of oil.
A large gas volume means that a given cc displacement of oil causes a small percentage change in gas volume = small pressure change = soft springing constant.
A small gas volume means that a given cc displacement of oil causes a large percentage change in gas volume = large pressure change = stiff springing constant.
Ok maybe not such a simple explanation but I don't know how to describe it any more simply
Anyway, you only have to look at the fact that when spheres age and leak gas pressure (pre-charge pressure is dropping with age) the suspension gets stiffer, not softer...
Regards,
Simon