A request by proxy, softest possible Xantia?

[macaroni]

A chap I know is trying to join this forum, but is having trouble, so he has asked me to post this request on his behalf, hope that's OK...


> Having come to a Xantia from two much-loved Peugeot 504s, I have
> some slightly different suspension questions, so I hope established
> members will bear with me.
>
> My Xantia is a 1999 TDSX automatic. In response to my request for a
> gentler ride, my mechanic - who is a Citroen specialist - fitted
> spheres intended for a 1.6 petrol model. This was less powerful, so
> the spheres gave a softer ride.
>
> Sadly, the result is still not nearly so smooth as the 504, so I am
> wondering just how much the Xantia can be tweaked. As a
> non-technical person, it seems to me that only four things can
> affect the ride:
>
> tyres
>
> total weight of the car
>
> spheres
>
> pressure in the hydraulic system.
>
> I have fond memories of a GS which I tried when they were current,
> and wonder just how far back one can go. For instance, is it still
> possible to obtain CX spheres, and would they function on a Xantia?
> A different thread wouldn't necessarily matter, as I could probably
> find someone to make up adaptors for me. Failing that, a close
> study of this forum suggests that XM comfort spheres might get
> nearer the qualities I'm looking for.
>
> I definitely prefer the ride in older cars. A friend has an Austin
> Cambridge A60 (a 1964 example), in excellent condition; we recently
> drove A60, 504 and Xantia around the same bumpy local roads, and I
> was happier in the A60 than in the Xantia. I realise that modern
> suspension is firmer to cope with the increased power, but I find
> it very uncomfortable. I feel the same about the Peugeot 405, and a
> friend's Audi A4.
>
> I hope there may be somebody out there who understands what I am
> trying to do, and can help me move my Xantia in that direction. I
> am willing to experiment with tyres, but I imagine that spheres
> would make more difference, so it seems sensible to investigate
> them first. (Rear tyres are Michelin Energy; front ones Corsa)
>
> On a slightly different matter: I believe my car has "anti-sink",
> but a minute or so after starting it rises a couple of inches -
> that's after standing for less than 24 hours. Does this indicate a
> problem? (The back rises first).
>
> Thanks in anticipation -
>
> LD

[Richard Gallagher]

My personal thoughts are that when anti-sink is fitted, the suspension does not get properly 'exercised' which causes stiffness within rear arm bearings and that the hydraulic struts are also not 'cleaned' by the seal moving through the full range of strut movement.

My evidence of this is that whenever I've bought a second hand Xantia, the rear suspension is always very reluctant to drop all the way to the floor when the height lever is moved to its lowest position, to the extent that in some cases it never dropped all the way, full stop.

My remedy has been to use Hydraflush for 1000 miles whilst performing "Citerobics" on a daily basis until the problem is solved. I then exrcise the suspension on a weekly basis to keep it supple which so far has worked well for me.

[Peter.N.]

I agree with you although many wouldnt! If its a '99 it will probably have hydractive suspension, in which case it is the centre spheres that are responsible for the soft ride, were they changed? you would never believe the difference. If they have and it is still hard it could be a fault in the electronics, but the first port of call is the spheres, as very often the centre ones are overlooked.

My Morris Oxford estate had a much better ride than any of the modern cars, but it did have crossply tyres, unfortunatly I dont think that they are available now!

Manufacturers seem to think that everyone wants to corner at 60 mph now and set up their suspension accordingly, it is very difficult to find a car now with a good ride. If you look at the Which? report, thert are I think only 4 or 5 cars out of all the tests which had a good ride and 3 of them were Jaguars and one was the Xantia.

[Mandrake]

> Having come to a Xantia from two much-loved Peugeot 504s, I have
> some slightly different suspension questions, so I hope established
> members will bear with me.
>
> My Xantia is a 1999 TDSX automatic. In response to my request for a
> gentler ride, my mechanic - who is a Citroen specialist - fitted
> spheres intended for a 1.6 petrol model. This was less powerful, so
> the spheres gave a softer ride.
>
> Sadly, the result is still not nearly so smooth as the 504, so I am
> wondering just how much the Xantia can be tweaked. As a
> non-technical person, it seems to me that only four things can
> affect the ride:
>
> tyres
>
> total weight of the car
>
> spheres
>
> pressure in the hydraulic system.

Add to that a whole host of other things - front struts (condition of wear of the shafts/bush and lubrication) rear suspension arm bearings, front suspension balljoints, front suspension lower arm bushes, ride height, and air bubbles in the hydraulic system. (For example from an air leak in the pump inlet hose, or a dying sphere bubbling the last of its nitrogen into the system...)

> I have fond memories of a GS which I tried when they were current,
> and wonder just how far back one can go. For instance, is it still
> possible to obtain CX spheres, and would they function on a Xantia?
> A different thread wouldn't necessarily matter, as I could probably
> find someone to make up adaptors for me. Failing that, a close
> study of this forum suggests that XM comfort spheres might get
> nearer the qualities I'm looking for.

Using spheres for one model on a different model is generally a very bad idea unless you REALLY know what you're doing, and the models are quite similar. (You could get away with using BX rear spheres on a Xantia for example as they are very similar)

It's a particularly bad idea to try and use CX front spheres on a Xantia as they have MUCH higher pressure (75 bars compared to 50) and much larger damper holes (1.9mm compared to 1.5) and you will get a ride that is dangerously floaty and unstable.

The reason a CX rides so well is not so much the spheres, but other mechanical design differences, like double wishbones instead of McPherson struts, softer rollbars (more body roll but more comfortable ride) and full body isolation from the suspension chassis.

> I definitely prefer the ride in older cars. A friend has an Austin
> Cambridge A60 (a 1964 example), in excellent condition; we recently
> drove A60, 504 and Xantia around the same bumpy local roads, and I
> was happier in the A60 than in the Xantia. I realise that modern
> suspension is firmer to cope with the increased power, but I find
> it very uncomfortable. I feel the same about the Peugeot 405, and a
> friend's Audi A4.

If you find the Xantia's ride bumpy compared to a 504, theres almost certainly something wrong with it. Although the ride doesn't compare to the older Citroen's like GS and CX, it's still streets ahead of most conventionally sprung modern cars.

> I hope there may be somebody out there who understands what I am
> trying to do, and can help me move my Xantia in that direction. I
> am willing to experiment with tyres, but I imagine that spheres
> would make more difference, so it seems sensible to investigate
> them first. (Rear tyres are Michelin Energy; front ones Corsa)

If your car is an SX it won't have Hydractive 2. A Hydractive 2 Xantia (VSX or Exclusive spec) has a MUCH softer ride than the standard Xantia, and nothing you do to the standard model will make it ride as well without compromising the handling. Sorry... if ride quality is really important to you, maybe look for a Hydractive 2 model ?

> On a slightly different matter: I believe my car has "anti-sink",
> but a minute or so after starting it rises a couple of inches -
> that's after standing for less than 24 hours. Does this indicate a
> problem? (The back rises first).

A minute is a long time. After standing over night an Anti-sink model should be up to the normal ride height in under 30 seconds. Many possible things could cause it to take longer, including a flat accumulator sphere...

Regards,
Simon

[Stempy]

I fitted XM spheres to the front of my Xantia which certainly improved the ride quality, not that it was that bad but now if floats along beautifully and handles just fine.

Like any suspension system though there has to be a compromise between comfort and handling. Check out the sphere specs on the GSF web site. They have a pdf with a table of all available spheres showing damping/volume/pressure ratios. You can then choose a sphere with a tad less damping and/or a higher pressure or volume. Possibly those recommended for a CX GTI Turbo. These are 500/75/1.65 and 500/40/1.25 compared to your current 400/70/1.65 and 400/40/1.1.

[Peter.N.]

You can get 'comfort' spheres for the XM from GSF, I dont know if they do anything similar for the Xantia. They make my XM ride more like the CX but not quite like it!.

[f00lzz]

I agree with you although many wouldnt! If its a '99 it will probably have hydractive suspension, in which case it is the centre spheres that are responsible for the soft ride, were they changed? you would never believe the difference. If they have and it is still hard it could be a fault in the electronics, but the first port of call is the spheres, as very often the centre ones are overlooked.

Hmm mine is a 99 TDSX and it isn't hydractive.. I think VSX and Exclusive are! I believe that 'comfort' spheres are available for Xantias.

[Peter.N.]

Ah! sorry,I keep thinking of XMs, all of mine have been hydractive but then they have all been been VSXs or equivalent

[Stewart(oily)]

There is also lubrication of the ride height linkages on the front and rear of Xantias which can help them to feel more supple, whenever I get underneath one it always looks dry and rusty.
Stewart

[FrenchLeave]

Forgive me if I'm wrong but I always understood that you don't need heavy damping under bump - it only makes the ride harsher - only under rebound, where it prevents float.

Also any size sphere, with any intitial pressure, will have the same pressure when supporting the weight of the car. In other words the front spheres under load will (must) each have a pressure of half the frontal car weight divided by the front suspension piston cross sectional area. This much is simple physics.

Similarly, nothing can be simpler than PV= a constant. So if you want soft suspension you are looking for maximum volume change for any bump load and this in turn suggests that spheres with the same initial pressure but a larger volume will give you a softer ride. This is, after all, the principle of hydractive suspension.

The downside will be increased roll. That's why hydractive was so clever, it gave you one without the other.

Regards, Derek

[Mandrake]

Forgive me if I'm wrong but I always understood that you don't need heavy damping under bump - it only makes the ride harsher - only under rebound, where it prevents float.

Actually, an interesting thing is that Hydropneumatic suspension typically doesn't have the 30/70 compression/rebound damping ratio that a lot of conventional spring/shock absorber suspension does.

Most of the non Hydractive models have symetric (50/50) damping where the threshold valves (the washers) are equal in strength and number in both in and out directions.

When you hit a bump the threshold valve opens and allows the bump to be absorbed, but then because the springing constant is so soft the rebound force is weak enough that it can't open the reverse threshold valve so the rebound returns only by the small bypass pilot hole.

The very soft springing gives a good seperation between the magnitude of bump forces and rebound forces - something you don't get with stiff springing. This good seperation allows a simple threshold valve to distinguish between bumps and rebound, and is one of the key things that gives a very steady/smooth ride.

This is also why when spheres get quite low on pressure and the springing gets stiffer, the stronger rebound force is enough to open the threshold valves, and the car starts to become bouncy and has a tendency to oscillate. (Stiffer springing also requires stiffer damping to keep things under control, and the threshold valves open too easily for the stronger rebound forces, so the bypass hole is no longer able to control the rebound)

The exception is Hydractive(2) models where they seem to have gone for a standard 30/70 split in the hard mode - you can tell its much easier to press down than lift up in hard mode. But in the soft mode it is pretty close to 50/50. (I've removed the central hydractive block damping valves before, and they're completely symetrical)

50/50 damping should give better ride than 30/70, (after all, not all "bumps" are upwards movements) but 30/70 has an advantage in cornering - it makes the side going down during body roll go down further than the lifting side comes up - thus moving the roll axis towards the inside of the corner, and causing an overall lowering in height during cornering.

Also any size sphere, with any intitial pressure, will have the same pressure when supporting the weight of the car. In other words the front spheres under load will (must) each have a pressure of half the frontal car weight divided by the front suspension piston cross sectional area. This much is simple physics.

Similarly, nothing can be simpler than PV= a constant. So if you want soft suspension you are looking for maximum volume change for any bump load and this in turn suggests that spheres with the same initial pressure but a larger volume will give you a softer ride. This is, after all, the principle of hydractive suspension.

Regards, Derek

Yep, a larger sphere (like an old DS one) with the same initial pressure will give a softer ride, and to get the same ride on a larger sphere you need a lower initial pressure.

What matters is what the gas volume is at the system operating pressure, and this can be calculated from simple boyles law.

The main advantage of a larger sphere is that it gives a larger operating range between minimum and maximum load, and this is why larger spheres are sometimes used on the rear of estates. (CX estates had 500cc spheres, the biggest of any model)

Regards,
Simon

[FrenchLeave]

Thank you, Simon.

So maybe Stempy's suggestion isn't so far out?

Incidentally, I've just changed the front centre hydractive sphere on my XM. It's a 500cc model at 70bar pressure and with a 1.5mm damper. And that's interesting because according to the workshop manual it shouldn't have a damper.

Regards,
Derek

[Mandrake]

Thank you, Simon.

So maybe Stempy's suggestion isn't so far out?

Incidentally, I've just changed the front centre hydractive sphere on my XM. It's a 500cc model at 70bar pressure and with a 1.5mm damper. And that's interesting because according to the workshop manual it shouldn't have a damper.

Regards,
Derek

Indeed it shouldn't!

There are two damper valves in the Hydractive control block. (One between the sphere and either side) I don't know about the XM but in the Xantia the damper hole in those internal damper valves is 1.1mm.

Sounds a bit like a front CX Turbo sphere you had there.

Adding an additional damper valve in series is likely to make the ride a lot worse than it should be...

Regards,
Simon

[FrenchLeave]

I missed a "2" out, the damper size should have read 1.25mm.

What's confusing here is the conflicting information that Citroen give in their own workshop manual:

Presentation Section on the late model V6. Front hydractive sphere; 450cc, 70 bar pressure, 1.25mm damper.

Section 09 Suspension, V6. Front hydractive sphere; 500cc, 70bar, 1.25mm damper. But looking closely at the accompanying drawing the arrow pointing to the damper points to the valve block so it almost certainly refers to the two integral dampers.

We seem to have strayed from the original subject matter, hope nobody minds.

Regards,
Derek

[macaroni]

No, please carry on. I am constantly amazed at the depth of knowledge on this forum.