C5 mods again - food for thought?

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C5 mods again - food for thought?

Post by Patxi » 28 Apr 2004, 15:12

Guys, my quest for the holy suspension continues [:D].
Since i changed the front shperes on my C5, the rear is always on my mind, bugging me all the time. (hey nice rimes, huh?![8D])
So, does anybody knows more details about the Estate rear spheres damping diametres?
I'm tempted to use the front shperes of the 2.0HPi (same pressure, but what about the dampening).
Other thing: if using , for instance, the former front spheres on the rear [:P] (55 or 51 bar - don't remember?) what should i expect, considering they have the "right" dampers? The rear is some 100Kilos heavier (or make it 200 pounds) than the hatchback; yet, the spheres on the hatchback have still lower pressure (31 bar)[?]
A bit O/T, why on some Xantiae the car often goes all the way up when putting the height lever on intermediate, when it shouldn't? It's someting i've never understood...
Thanks fellas!

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Post by AndersDK » 28 Apr 2004, 16:50

Hi -
It makes sense you have a lower wheel sphere pressure if the axle has less load.
There is a direct relation between weight on wheels and sphere pressure. The aim is to have the sphere membrane located approx midway between the sphere's gas & hyd oil cavities, as this gives equal excursions for the wheel bouncing up/down.
As for damping, it's quite a bit more complex. Especially if active control of the suspension is involved ...
But my own rule of thumb tells me that you must also have harder damping on wheels with a higher load, as then the energy involved in suspension excursions is larger.
The way damping is done on Citroen spheres is by 2 means :
1) the center bore you can directly see (at least on earlier systems)
2) the valves constructed by flexible steel discs.
The center bore decides the immediate "soft" feeling on the spheres during drive, as this sets the immediate flow rate in/out the sphere's hyd oil cavity.
The bore can not react to HI-amplitude suspension accelerations, because of the set flowrate. This would give a harsh feeling suspension.
Thus the disc valve opens and admits for extra flowrate, letting the sphere's gas cavity absorbs HI-amplitude accelerations (within sensible design limits), and allows for continued comfort.
Logic tells you that both the bore and the valve must be calibrated to the factual suspension requirements for axle loads and expected speed (suspension accelerations) of the vehicle.
I'd expect that using front wheel spheres on rear wheels gives 2 distinct results :
1) the initial higher sphere gas charge pressure makes for more jerky ride, as the effect equals a longer suspension spring. Risc of "bottoming out", when wheels down bounces, as the sphere membrane is closer to the hyd oil cavity inner wall. May instead give a bumpy ride because of this.
2) the damping would be less, as there is less energy needed to dampen from the initial calibrated dampers, thus leading to un-stability, or in fact amplifying the jerky feeling.
Please shoot down anyone, as it's in-tolerable to be stuck in wrong assumptions [8)]