xantia_v6 wrote:
Another point to ponder is the damper elements. The Xantia dampers have different marking to the XM, but for both models the front and rear dampers have the same markings, likewise the front and rear hydractive assemblies (including the dampers) have the same part number. This (surprisingly) seems to indicate that the centre sphere damping is the same front and rear.
Yes that's correct, however keep in mind that the centre spheres never work in isolation like the strut spheres do - the soft mode is centre and strut spheres connected in parallel providing two flow paths for the oil from each strut to take.
So the overall characteristic of the soft mode is an amalgam of strut and centre sphere gas pressures and damper valves. So even though the damper valves in the hydractive blocks front and rear are the same that doesn't mean the damping characteristics are the same in the soft mode front and rear, because the strut spheres differ so much.
Also the gas pressures of the front and rear centre spheres also differ considerably, so the effective damping Q factor is different even for the same damper valve. A lower gas pressure at the rear gives a stiffer springing rate, which will give a higher Q to the damping of the damper valve - however that assumes that the leverage ratio of front and rear rams is the same, which they're probably not - and I haven't sat down to work out the ratios of the front and rear suspension to figure out which way they differ.
If the damping is that un-critical, why do XMs and Xantias need different damper settings? The weight of the cars is not that much different.
I don't think its right to say the damping is uncritical just because the front and rear damper valves are the same - as I described above the tuning front and rear is still different in soft mode. However why XM and Xantia valves differ and in what way I don't know.
This reminds me of another oddity (which I have mentioned before), that the Mk1 Xantia V6 was fitted with XM damper elements at the front, but the Mk2 Xantia V6 reverted to Xantia damper elements. Why? and what difference does it make?
Good question. My Mk1 and Mk2 V6's both rode quite different to each other, even with recently replaced spheres, however in my experience no two models of Hydropneumatic Citroen ride the same even if they are the same model so it's hard to know if it was model related difference like the one you suggest, or just variations in the individual cars!