Ride quality

[casalingua]

As long as I´ve had my XM Si and SEi, I´ve noticed how cattle grids defeat the suspension. The front wheels glide over the grid like it´s not there but the rear suspension passes all the vibrations through. However, today I noticed something astonishing. I was driving over a long section of pavement painted with thick white stripes which were transverse to the car, just like a cattle grid. Sure enough the rear suspension thumped horribly as it would for a cattle grid. But, since it was a very long section, there was time for the rear suspension to change its behaviour and for the remainder of the striped pavement (about thirty metres) there was no noticeable vibration at all. So, the rear suspension can, if given enough time, go so soft that it completely masks these transverse ripples. Does anyone know how one could reprogram the suspension to avoid this cattle grid defect? Or is that impossible? Do your cars do this? Or is mine faulty? I´d like to note that in everyother way the car drives like it should and fully maintained. If I drive the car over something like an unmetalled road, it´s fantastic. Or a motorway. It just hates urban-type irregularities like cracks and manholes and asphalt scabs.

Richard

[robertmnorton]

Hi Richard, you've pretty well nailed the nature of the beast, and one of the probable reasons the xm was not received with the affection of it's forerunners. There is no real solution from the electronic angle. Damper orifice, pressure and volume changes of the spheres can make a difference but with compromises to overall handling in both modes.
robertm

[casalingua]

Thanks for the answer. Where does one find out the specification for the revised damper orifices and other mods? Is it a matter or obtaining some off-the-shelf bits? And what are the deficiencies of the change? I would tolerate a lot more body roll if I could improve town driving. I don´t tend to drive the car like it´s a sports-saloon anyway.

Richard

[robert_e_smart]

You can fit spheres from different cars to give different caracteristics. Different pressures, volumes, damper sizes.

Some people have fitted Xantia non hydractive spheres to their Xms. I haven't so can't comment.

If you search for some of the sphere tables you can view all the sphere specs and compare them.

[Jan-hendrik]

You could enlarge the damper orifices, but that would be an irreversible solution. Sphere tables can be found in this document:
http://koti.mbnet.fi/svc/doc/Citroen/Xa ... ndbook.pdf

[Peter.N.]

I had this problem when they first built the new A30 to Exeter, it has a ribbed concrete surface that was very noisy and was the source of numerous complaints by local homeowners at the time, I fitted a new pair of centres spheres and the problem all but dissapeared.

Peter

[kenhall]

My preferred setup on my 2.1TD hatch is with IFHS Comfort spheres (AKA AMTEX) on all four corners and leave the suspension setting on Sport all the time. An LED indicator on the dash tells me when the system switches between soft and firm and although I would describe my driving style as 'brisk' I estimate that for well over 90% of the time the system stays in soft/normal mode. It does beg the question why the Normal setting is there in the first place (on the Mk2 XM).

For the benefit of anyone experimenting with sphere characteristics I recently I fitted a full recharged set of spheres (previous self recharged set was still within pressure tolerance after 3 years)and took the opportunity to measure the damper orifice sizes in the Comfort spheres and the results are as follows:

Front suspension sphere (SPCXMSF type) Volume 400cc, Pressure 75bar, 1.5mm orifice (CX saloon used 500/75/1.65 but didn't have hydractive of course)
Rear suspension sphere (SPCXMSR type) Volume 400cc, Pressure 40bar, 1.1mm orifice (CX saloon used 500/40/1.25 but didn't have hydractive)
I don't know if any other characteristics of the dampers differ, eg the spring discs.

BTW I used a set of Microbox HSS twist drills (0.3 - 1.6mm) to measure the orifice diameters - but be warned if you buy a set, the nominal sizes are imprecise and checking with a caliper/micrometer is recommended for accuracy.

Ken

[robertmnorton]

Hi Richard, there is a huge selection from the available charts. My personal view from the tables is that the 500cc 40bar 1.0mm spheres fitted to the rear of the BX TZD would give the compromise with the standard XM fronts as a starting point, but there so many permutations. If you were able to charge spheres yourself you could experiment, but the experience of the members on the forum would be the best way forward. I haven't tried any of the non-xm spheres but currently run with XM front spheres on the rear and accumulator spheres on both hydractive valves. From a personal perception this has improved comfort levels and retained stiffness during brisk A & B road driving.
robertm

[Dieselman]

If the suspension eventually becomes soft and pliable when traversing these ridges it suggests that it has gone into hard mode when the front of the car has passed over them, but switched back into soft mode after 3 seconds.
As a test, disconnecting the speedometer pick-up or the body motion sensor should force soft mode.

[DerekW]

Irrespective of which sphere pressure you start with. the pressure in the spheres is always the same when the car is stationary on its wheels (car weight on that corner divided by area of suspension leg piston or ram). To give soft suspension you need the maximum gas volume and a reasonably high charge pressure, not too high because you must allow for rebound movement. So 500cc spheres with a charge pressure at or a little higher than standard sound like the bee's wotsits.

This should be true for all four corners.

Derek