C5 ride

[Peter.N.]

After having recently driven my XM which I don't often see as my son has adopted it, and returned to the C5 the ride on the latter is definitly not as good. There seems to be a fair ammount of suspension movement especially on the rear but the car rocks from side to side on uneven surfaces, the XM rides almost flat and is fitted with comfort spheres.

Is there anything I can do to improve the ride? The car has covered nearly 150k and quite possibly still has the original spheres, do they make comfort spheres for the C5 or can I fit XM ones, all suggestions appreciated - well most anyway.

Peter

[citronut]

After having recently driven my XM which I don't often see as my son has adopted it, and returned to the C5 the ride on the latter is definitly not as good. There seems to be a fair ammount of suspension movement especially on the rear but the car rocks from side to side on uneven surfaces, the XM rides almost flat and is fitted with comfort spheres.

Is there anything I can do to improve the ride? The car has covered nearly 150k and quite possibly still has the original spheres, do they make comfort spheres for the C5 or can I fit XM ones, all suggestions appreciated - well most anyway.

Peter

turn it into a cube

what does it feel like if you lean on either end with the engine running, you should be able to tell if the spheres are past there best this way

[JohnD]

can I fit XM ones,

Came across this on the 'net. Can't say as to the accuracy of what's said.


You can't fit Xm/xantia spheres on a C5/C6 the new hydraulic system uses different fluid -LDS- and is completely incompatible with the old LHM based system. As for the "difference" in spheres sizes, the Xm used 400cc/50bar spheres at the wheels and 500cc/60bar center. The C5 uses two 385cc/44bar spheres and a central 385cc/62bar sphere, the difference is not as big as it's made out to be, since the strut pistons do differ, which has a bigger impact.
The bigger strut pistons lower the static pressure, which means that the static volume remains larger. You are correct in saying that the bigger bumps cause increased stiffness. This progressive spring behaviour is the reason Citroëns have such great roadholding on bad surfaces. The fact that this effect is larger on the C5 is also moslty due to the larger strut pistons. The result of all of this is that in soft-mode the C5 is about 20% harder than an Xm. In hard mode 18%. The difference between soft and hard mode is about 60%. In numbers:
Xm H2 = ~0,8 soft
C5 H3+= ~1,0 soft
Xm HP = ~1,1
C5 H3 = =1,25
Xm H2 = ~1,3 hard
C5 H3+= ~1,6 hard
As you can see a C5 without hydractive 3plus is almost as hard as an Xm in hard-mode. It is technically possible to replace the outside spheres on a Hydractive 3plus car (44bar) with those from a regular C5 (57bar) This will bring soft mode closer to the Xm, but the effect on hard-mode is more pronounced, as it would become too soft, which may be
dangerous in extreme manoeuvres.

[Peter.N.]

Mmmm.. The rear suspension feels quite soft when you bounce it with about 6" of movement but it still feels hard wjen the back wheels go over a bump. Any idea how long these spheres are supposed to last?

Peter

[Citroenmad]

The place I get a lot of Citroen spehres from do say that the C5 can use Xantia/XM spheres. Im not sure about this as I always thought the same as JohnD said.

I recently drive a fully hydractive (like your 2.2) C5 which had comfort spheres fitted to the corner spheres only. It did ride really very well indeed, very supple.

There are a few problems with trying to improve the comfort of a C5s suspension.

First is what your experiencing, the rocking motion over indivitual bumps. This is due to the C5 having a very thick anti-roll car. I know people have been testing softer roll bars from other cars. I would guess the basic and most early C5 (say a 1.8 petrol LX) will have a weaker ARB than a 2.2 SX. It might be worth looking into, as that is the worst part of a C5s ride. WHen I changed a drop link on our C5 estate I drove the car around the block with the NSF drop link missing. The ride was really something else, better than an XM on individual bumps. It would drive up and down the low curb which leads to my driveway without even feeling it.

Second is suspension travel, its struts dont have the movement (drop) which the Xantia and XM have, so this causes a slightly worse ride and the odd thunk over continious speed bumps. This is normally fine as the suspension is set up with this suspension movement. However, try and make a C5 softer and you will realise the suspension travel is much shorter than it possibly should be. Our first C5 had a very nice ride (not sure if it had comforts or what) but over undulating roads at speed it would fine the top and bottom of the travel quite easily, often resulting in the rear mudflaps meeting the road - However I never hang about!

Third, spheres. To be safe C5 spheres should be used, as there are so many different opionions about using XM spheres on them due to the different fulid. I think it would be very interesting to try this out, I fail to see that LDS will ruin the diaphragm in the spheres. So C5 spheres leave only the comfort spheres, which are C5 spheres will enlarged damper holes. This is not the correct way to improve ride quality, as damping will be reduced. Ideally damping should stay the same but the sphere should be softer - with more gas. Which leads me into Xm/Xantia sphere testing. However, the softer it is the more suspension travel is needed ...

Also, since you have a hydractive C5, you could always fit the corner spheres from a non hydractive, which should give an increased ride quality.

So, anti-roll bars and spheres need to be played around with, but there is certainly potential.

C5 spheres were supposed to last 5 years or 125K. However I have known ones last no where near that and others which are still excellent. You can pressure test them in the usual way.

[Peter.N.]

Thanks for that Chris, very informative. Would the 2.0 Hdi have a thinner anti roll bar? That was the one I wanted, I only got this one because it was very cheap, I would prefer a 2.0 on fuel consumption grounds alone. I know what you mean about suspension travel, I drove off the end of our concrete track a bit fast and hit a stone which smashed the sump, I have only just got it back on the road again today.

I did drive a 2.0 a few weeks ago but not on the rough tracks that we have here so couldn't really do an accurate comparison, I will have to try another 2.0 and make a careful note of the ride before I decide what to do.

Peter

[Citroenmad]

I think early 2.0HDi 8vs do perhaps have softer ARBs, however I have not checked the thickness. I should check our eldest C5 with our newest C5, as the newer ones roll much less but have a firmer ride.

There is an article in the September Citroenian which you might be interested in, so I will copy a bit in here. This is about the current C5III, but it is the same idea:

"C5 front roll bars go from 23.5 to 25mm, rear 20mm to 21.5mm, the largest bar is 28% stiffer than the smallest one"

There is also a comment from the writer who is going to get the weakest ARB he can find to fit his C5 and give that a test.

It is true that ARBs ruin ride quality as it effectively joins one wheel to the other. If you dont press on through corners then a weaker anti roll bar will be a real advantage to ride quality.

[citronut]

here are the anti roll bars listed for MK1 and MK2 C5's

5170 C0
R/ANTI-ROLL BAR
DIAM 21,5
- 5 DOOR SALOON

5170 C2
DIAM 22,5
- 5 DOOR SALOON
DIAM 22,5
- ESTATE

the other thing that can stop the rear suspension moving freely is rear arm bearing collapsing

[Peter.N.]

Thanks for the further info. The rear suspension moves freely enough with about 6" of up and down movement - just doesen't absorb the bumps very well.

Peter

[Citroenmad]

Thanks for the further info. The rear suspension moves freely enough with about 6" of up and down movement - just doesen't absorb the bumps very well.

Peter

That'll be the anti roll bars then

[Spaces]

If both wheels go up at the same time then the anti-roll bar should have no effect on the suspension's articulation. Most rougher roads with smaller bumps don't act evenly on axles, foundation undulations are much more likely to do so. Perhaps you feel the decent amount of rear travel working better over undulating roads than over rough roads with smaller irregularities? Being a hydractive car it's possible something in the hydractive system is not working properly, cutting out the centre spheres too rapidly? Maybe it's just that the spring rates and stiff arbs just poorly matched to our roads? Nothing worse than the rock-roll effect created by over-stiff arbs as your heads is knocked left and right quite rapidly as the wheels encounter individual bumps.

Weaker arbs may not reduce cornering limits at all if the originals are on the stiff side of ideal, but actually increase them as the load is spread better over both wheels on the axle and bumps aren't transmitted across the axle. Modern French roads are very different from our own, with smooth surfaces and decent foundations - modern PSA cars seem to try to exploit these to the full. As I probably mention in this thread, the arb may work well on a constant, smooth surface with constant radius and grip - but how many roads do you know of like that in England?

I'm not knocking Citroën's efforts at suspension under Peugeot (no pun intended), it is almost impossible to follow genius especially where engineering is deliberately and hugely compromised and little or no R&D takes place. The Hydractive system is a great way to overcome a cheaper family car's compromised design and I love it - you don't know how effective it is until you step into a non-H model. But... a stiffly-suspended body which is bucking around following a road's bumps is a huge impediment to going really quickly - the extra inertias involved with bodyshell and its payload moving up and down unnecessarily place enormous extra loads on the suspension, which compromises its abilities. To an extent, wider and lower profile tyres cope when there is plenty of grip but as soon as conditions deteriorate, things rapidly become much worse.

Living where we do, where traffic is minimal except in the peak holiday season, roads are quick but often poorly surfaced, have poor foundations, frequently not only standing but running water as well as many frost pockets, a well-balanced motor car with fine suspension makes itself very obvious. As always, fine articulation, strong location of suspension, geometries which maintain themselves regardless of load or displacement and careful attention to detail shine through. I once drove a friend's car with over-strong arbs and it was comical the way it tried to deal with a demanding surface, corners, poor foundations and standing water. Saab 99s and 900s did without them altogether (unless turbos) but didn't heel unnecessarily through faster corners - they relied on fundamentally good engineering in the same way Citroens once did. The recent McLaren MP12-4C sports car does without also, using a system of hydraulics and accumuators which were inspired by Citroën and developed by a small Australian engineering company. Lotus similarly understood suspension and created cars which would traverse huge foundation irregularities at high speed in a very level, Citroën fashion. Many of the more upmarket manufacturers are at the minimum decoupling arbs, using a variety of systems.

So weaker anti-roll bars could be a huge improvement (I would fit the weakest available for a diesel and go from there), but I would be cautious of replacing just the one - the relative strength of the two is critical in the handling balance. I know you don't drive to end it all, Peter, but you never know when you may have to swerve rapidly on a wet road, to avoid a cyclist, deer or other obstacle in your path. Perhaps it would be worth setting the Hydractive to remain in soft mode and seeing how bumps are taken then?

[Mandrake]

Good point, don't change just one anti roll bar as that will upset the handling balance. For example if you fit a softer bar at the front and leave the rear the same it will bias the on limit handling more towards oversteer which may cause the rear to let go first, especially on rough surfaces - a potentially lethal situation.

Citroens usually have both softer springing and softer anti roll bars at the rear to ensure that the rear grips well on all surfaces and does not let go first. Even though this can lead to an on limit under steer characteristic it is much safer than the rear letting go first as can happen with some other cars with supposedly better handling.

In all the years of driving Citroens hard I've only had the rear let go on me once - and this was on loose gravel where I braked instead of accelerated on a corner (hey I was only 17 at the time ) causing the rear to swing right out resulting in a fishtail ending in me facing the opposite direction in a ditch. (This was in a GS by the way Spaces...)

I never managed to push the rear end of my previous 2.0 HA2 Xantia to let go, even though it was frequently driven near the limit. Very good handling in that particular car, and very stable and safe at the limit. (Excellent 205/60/15 Michelin XM1 tires all round probably contributed a lot)

I would certainly be wary of changing the suspension balance between front and rear in any way.

[Peter.N.]

Spaces

I'm fairly convinced now about the anti roll bar stiffness being the problem, I gave a lift to a friend yesterday who suffers with back trouble and does a lot of miles, he has has several cars since I have known him but he said 'this is what I need' and has asked me to look out for one for him, I suppose I could always sell him mine and get a 2.0L yes on a good road it does ride well but particularly on our top track, which I think you are familier with , the 'lurching' is noticably worse than in the XM.

Mandrake

I have never pushed a hydropnumatic to the limit, I don't drive like that (any more ) and I have driven them for for nearly 20 years, my driving would suit four accumulator spheres at the corners and cross ply tyres but I do appreciate the need for some sort of stability - in the car as well.

Peter

[cachaciero]

Interesting I know what Peter means by "rock n' roll " a characteristic with which I am very familiar in my estate and it doesn't take much to get it to do it, seems to me that softer ARB's is a good way to go, although in my case as my C5 ownership days are nearly over it won't be done on mine.
One thing I would say re LDS / LHM component and seal wise there is no difference, all hydraulic components will work equally as well with both oils, in-fact the C5 sphere first saw the light of day on later LHM Xantia's.
LHM and LDS are produced to the same hydraulic spec and are identical in that respect, the only difference is that LHM is a semi-synthetic base and LDS a pure synthetic base so in the longer term LDS will likely take longer to breakdown and not be so susceptible to the formation of "sludge".
This may be important in a C5 system as there are no cleanable / replaceable filters in the hydraulic system to catch any sludge, however on the other side the oil in a C5 does not get worked to anything like the extent of the oil in a XM or Xantia so LHM in a C5 may not breakdown anyway.

cachaciero

[Spaces]

There's only one way to significantly improve on the Citroën hydraulic suspension and that is Chris Heyring's Kinetic system - Hydractive is clever but doesn't really stretch the thinking any further, it simply makes for a more adjustable system and tries to make up for a wide track, low centre of mass and decent suspension design.

Heyring's technology was bought by the US in 1999 and has been banned in various motor sports because of its enormous benefits. As we know, Heyring was inspired by the hydraulic suspension put into production in 1955 by Citroën and in to my mind is the first new and exciting suspension development since, a major advance in suspension tech, not just an add-on for top end 4x4s and sports cars.

As such, I think we gas/hydraulic suspension-lovers should be slightly nutty about Heyring and his ideas - and wondering how to integrate one of his systems into a Citroën. I love the comment from Chris/GreenBlood on the aussiefrogs forum - here and was a little surprised at the lack of response to this thread - A 21st Century Paul Magès given the apparent enthusiasm for every other Citroën-derived hydraulically enhanced suspension.

I love this comment from a Toyota owner with a very basic Heyring set-up which still uses a steel torsion bar but can decouple it with hydraulics, "A 200 without KDSS is like Xmas without Santa!", here.

How lovely it would have been to pass the Heyring solution to Citroën in the 50s and 60s to integrate with their existing hydraulics. It wouldn't surprise me if something almost identical hadn't been talked through. I'm getting brain fade trying to figure how it could be done.

Here's someone else's description of the system as fitted in the McLaren MP4-12C.

It is the ability to separate the different modes of roll motion and articulation motion which is key - with an pressured accumulator connected in each circuit to control the amount of roll stiffness. The current systems as in the McLaren are electronically controlled but the originals were completely passive. It is the simplicity of the design combined with the enormous improvement in ride which I find so attractive. Tenneco is complicating the basic design as they integrate it with their existing electronic damper control, with the aim of having a pumped system by 2015, see here.