Theoretically Speaking

rossnunn · Post by **rossnunn** » 30 Nov 2005, 20:16

Could you fit the Hydospastic suspension to a ZX?
The only real headache I can see would be the front strut towers.
The rest is just extra hangers, brackets & pipework.
I thought (see any light dim?) get a C5 with that has the ver 3+ on it (a rolled one would be perfect) & use all the gubbins from that, mainly because it has the later 'Active' setup & it doesn't use a big leaver just some buttons.

Your thoughts pls

jeremy · Post by **jeremy** » 30 Nov 2005, 20:32

All powered by what size of engine?

I think my 'abandoned project' sensor is beginning to bleep!

Hydrolastic should not be confused with Citroen's hydropneumatic system. the hydrolastic system as used by BMC produced good riding and good handling cars in the days of very soft and wooly cars. The weakness of the system was its load compensation - generally the use of steel springs at the rear. What it did do was to link the suspension of the wheels on one side which I believe but am not certain the 2CV managed but without computers the hydropneumatic system does not.

Interestingly the current Citroen rally car seems to use a system that links the wheels on the same side like hydrolastic. This system I believe originates in Australia.

rossnunn · Post by **rossnunn** » 30 Nov 2005, 21:23

sorry hydropneumatic then

the engine shouldn't be a problem, look at the range thats in the XM / Xantia alone.

alan s · Post by **alan s** » 30 Nov 2005, 21:26

Read all about it; make you wanna cry.

http://www.kinetic.au.com/

Alan S

DoubleChevron · Post by **DoubleChevron** » 30 Nov 2005, 21:39

Why ???

Just buy a GS/DS/CX/SM ... Not only will you have a *proper* Citroen, you will have a car that could probably be used right away, and the hydraulics are already there.

Isn't a ZX just a Poogoe

seeya,
Shane L.

rossnunn · Post by **rossnunn** » 30 Nov 2005, 22:12

why not? its something different.

Mandrake · Post by **Mandrake** » 01 Dec 2005, 04:13

alan s wrote:Read all about it; make you wanna cry.

http://www.kinetic.au.com/

Alan S

Very interesting, I wasn't aware that the WRC Xsara was using a system like that.... now I see why Citroen has probably pulled out next year - they need time to finish off their next rally car minus the banned suspension system

Is there another site with a bit more technical info/diagrams than that one ? It's a little bit elusive about any hard facts, and you can't QUITE follow the working of the systems from the simplified diagrams they have there...

Regards,
Simon

Mandrake · Post by **Mandrake** » 02 Dec 2005, 06:03

One more comment - am I right in thinking that the Activa - which came out in 1995, and has prototypes as far back as 1989, effectively has this same principle of rollbar coupling ???

If you look at the diagram for the Activa, the front and rear rollbar rams are actually connected to each other via the "SC/CAR Regulator" in the soft roll mode, in a way that would cause increased roll resistance, but reduced resistance to "axle crossing". (Thus improving ride and tyre contact on uneven surfaces)

So if I'm right the Activa already incorporates a version of this technique and could be one of the first production cars to ever use it ? (Let alone one of the first to have actual active anti-roll correction on top of that...)

Regards,
Simon

citronut · Post by **citronut** » 02 Dec 2005, 08:14

jeremy wrote:All powered by what size of engine?

I think my 'abandoned project' sensor is beginning to bleep!

Hydrolastic should not be confused with Citroen's hydropneumatic system. the hydrolastic system as used by BMC produced good riding and good handling cars in the days of very soft and wooly cars. The weakness of the system was its load compensation - generally the use of steel springs at the rear. What it did do was to link the suspension of the wheels on one side which I believe but am not certain the 2CV managed but without computers the hydropneumatic system does not.

Interestingly the current Citroen rally car seems to use a system that links the wheels on the same side like hydrolastic. This system I believe originates in Australia.

no 2CVs susp is not linked on one side apart from both springs on each side sharing the same can, the susp is fully independant on all four legs
,also the i would have thought the front hydraulic struts would be the easyes part of the swop,i agree the engine size should not be a problem as the BX dose run the 1.4 TU lump
regards malcolm

jeremy · Post by **jeremy** » 02 Dec 2005, 08:20

What's particularily interesting is that Citroen hydraulics were used on Peugeot rallycars in the 80's, the activa system has been developed and then they use the Kinetic system which is passive and gives much the same results appartently as the Activa in their all conquering rally car but apparently make no use road cars.

All very strange but is it?

A little while ago I mentioned on here the problems my Father is having with an air suspended Range Rover and (Fastandfurryous I think) suggested I converted it to Citroen hydropneumatics. I think the two systems are rather different in that the Citroen system is designed to optimise suspension performance over a relatively small range of travel while 4WD systems require very large axle movement and 'articulation' to cope with muddy tracks and so on.

So is one reason why Citroen have used Kinetic suspension that it permits greater wheel movement than Activa and is therefore more suitable for a rallycar.

The next question is could they use it in the rumoured 4X4 - which could be badly in need of some unique feature if its not to be just another one among many?

Mandrake · Post by **Mandrake** » 02 Dec 2005, 09:25

jeremy wrote:What's particularily interesting is that Citroen hydraulics were used on Peugeot rallycars in the 80's, the activa system has been developed and then they use the Kinetic system which is passive and gives much the same results appartently as the Activa in their all conquering rally car but apparently make no use road cars.

All very strange but is it?

Yes and no. As far as I know the WRC rally rules in recent years have prohibited active suspension systems, which basically rules out any version of the hydropneumatic system - and naturally Hydractive or Activa.

Because Kinetic's simpler "RFS" system is basically a passive system, despite having a hydraulic connection between the front and rear rollbar, they got away with it being classified as a passive system and thus allowed in the rules.

Obviously there are some sore losers in the WRC because the rules have just been changed to exclude systems that connect the front and rear rollbars in any way

A little while ago I mentioned on here the problems my Father is having with an air suspended Range Rover and (Fastandfurryous I think) suggested I converted it to Citroen hydropneumatics. I think the two systems are rather different in that the Citroen system is designed to optimise suspension performance over a relatively small range of travel while 4WD systems require very large axle movement and 'articulation' to cope with muddy tracks and so on.

I wouldn't say that the Citroen system is optimized for small amounts of travel - quite the opposite. Look at the amount of suspension travel on a DS, or a CX - both are simply MASSIVE compared to any other passenger car. Watch the eyes of any nearby motorist pop out if they see you lifting and lowering it through the full suspension travel. 8)

Admitedly it is still less than an offroad 4WD, but you wouldn't really expect any passenger car to have that much travel.

On the other hand the GS, BX, and Xantia have relatively modest amounts of travel compared to a DS or CX, and although still more than average aren't that much more.

Any of the earlier Citroen's with softer rollbars (again, DS and standard CX's are a good example) have excellent articulated movement and are remarkably good at navigating difficult, uneven ground, (in fact even a GS does this pretty well) however some of the later models with stiffer rollbars suffer from the problems that the Kinetic system is designed to avoid. (Too much load transfer from one wheel to another and torsional strain in the body)

Because of the side to side hydraulic connection, the springing of the spheres themselves don't limit any slow articulated movement over uneven surfaces, only the rollbars are guilty of this, unlike a conventionally sprung car where even independant springs without a rollbar will resist free articulation.

Hydractive 2 partially overcomes the problems of the rollbars - because the centre sphere adds maximum additional softness to single wheel independant movements, 50% softness to bumps that are equal on both wheels (such as judder bumps) and adds NO extra softness to roll movements - as no oil flows in or out of the centre sphere during roll, you only get damped side to side flow passing through the two damper valves.

This means that in hydractive 2's soft mode the normal negative effect on single wheel bump absorption of a conventional rollbar is significantly reduced compared to an equivilent plain hydropneumatic or sprung system giving equal roll stiffness. In other words a much better vertical ride (and also better articulation) for a given amount of roll, and this doesn't even take into account the ability to switch into hard mode when needed where roll is drastically reduced again.

Still not as good as interconnecting the front and back rollbars like the Activa or Kinetic system though.

So is one reason why Citroen have used Kinetic suspension that it permits greater wheel movement than Activa and is therefore more suitable for a rallycar.

Personally I think the Activa suspension perhaps in slightly retuned format would be fantastic for rallying, however I fear that its probably just a case of hydropneumatic suspension of any kind being outlawed by the rules.

After all the DS, SM, and CX were all rallied in their eras and did very well.

But as I query in my previous post, does the Activa actually have an equivilent to the Kinetic system in disguise ? It sure looks that way to me when I study the interconnection diagrams.

The way they're piped is such that the oil flow of the front of the car trying to roll will oppose the oil flow of the rear trying to roll the same way, and cancel out, leaving only the rollbar stiffness itself, exactly like the Kinetic system.

Except in the Activa it goes one step further and "twists" the rollbar back in the opposite direction to cancel the natural roll of the rollbar.

Warp movements caused by uneven ground, where the front and rear "axle lines" tilt in opposite directions will cause oil to flow freely and thus the suspension will move more easily in this mode than conventional Hydractive 2 with conventional side to side rollbars. Couple that with the side to side piping of Hydractive2 which would also allow more easy tilting of the "axle lines" and in theory the Activa should have better slow speed uneven ground articulation than the simpler Xantia's....

Has anyone ever done any testing of this ? Driving an Activa on 4WD type surfaces ?

Regards,
Simon

Mandrake · Post by **Mandrake** » 02 Dec 2005, 09:30

citronut wrote:no 2CVs susp is not linked on one side apart from both springs on each side sharing the same can, the susp is fully independant on all four legs

Are you sure ?

I was under the impression that the springs are joined end to end, and that the junction point of the springs is only loosely coupled to the body thus allowing the centre point of the two springs to move back and forth a certain amount.

Regards,
Simon

jeremy · Post by **jeremy** » 02 Dec 2005, 12:52

Interestingly I see that the forthcoming Citroen 4 X 4 is to be built in partnership with Mitsubishi who apparently are developing a chasis for it.

Mitsubishi won the Paris-Dakar rally with a Pajero with guess what - yes Kinetic suspension.

Wonder if this Pajero chassis is goint to find a use in production.

It also seems Kinetic is used on some Lexus 4 X 4

http://www.prnewswire.co.uk/cgi/news/release?id=115442

fastandfurryous · Post by **fastandfurryous** » 02 Dec 2005, 13:15

jeremy wrote:A little while ago I mentioned on here the problems my Father is having with an air suspended Range Rover and (Fastandfurryous I think) suggested I converted it to Citroen hydropneumatics. I think the two systems are rather different in that the Citroen system is designed to optimise suspension performance over a relatively small range of travel while 4WD systems require very large axle movement and 'articulation' to cope with muddy tracks and so on.

That was actually a bit of a joke! The engineering you would need to fit Hydropneumatic suspension to a range rover would be fairly interesting, and the piping work would be legendary!

Although Range-rover front suspension actually only has a travel of 8", you would run in to problems with Sphere-type suspension, as you may not have enough travel in terms of sphere volume, and end up having to use uktra-rare 700cc spheres from the rear of a CX estate or something similarly silly. After all, although the front suspension travel of the CX is measured in miles, but you can't use all of that travel at once: the volume of fluid in the cylinder is way more than is available from the sphere, thus the sphere would top out before the physical suspension.

As to the range rover air suspension.. it is a known nightmare. Companies have "sprung" up all over the place (pun fully intended) who will remove the Air suspension and fit normal springs and dampers. It's not a hard job to do yourself though.

jeremy · Post by **jeremy** » 02 Dec 2005, 15:04

I appreciate it was meant as a joke which is why I didn't open the subject when the posting was made. I was just using it as an example of the different requirements for suspension systems. The Range Rover is still awaiting repair and somehow I think may come my way at Christmas time when I'm made redundant. (Not by way of a Christmas present I hope as while I like Land Rovers - particularily series vehicles I can't stand Range Rovers which I've always regarded as grossly overweight and rather poor machines which drive like a blamanche.)

Its rather amusing really that in 1993 someone paid £30 - 40,000 for this thing and when you look underneath the front swivels are the same things that have leaked on Land Rovers since 1948!