Theoretically Speaking

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

User avatar
Mandrake
Posts: 7790
Joined: 10 Apr 2005, 17:23
x 194

Post by Mandrake » 02 Dec 2005, 20:23

fastandfurryous wrote: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.
Huh?

What makes you think you "cant use all of that travel at once" ? You're completely back to front about that.

The volume of fluid in the cylinder is not whats important, its simply the cc displacement which is important, just like an engine, bore size (which is 35mm on a CX if I remember right) times stroke, which is approximately 60 - 70mm, even though the total suspension travel is approx 200mm - don't forget about the large amount of upper arm leverage on the CX, which is at least 3 to 1.

The displacement in the cylinder is NOT more than the capacity of the sphere, in fact nowhere near it. If we take the 35mm and 70mm figures to be accurate, thats 67cc displacement - compare that to the 500cc capacity of CX front spheres, and thats only 13% of the sphere capacity.

Even just thinking about it without calculating it, there is no way what you say could be true - otherwise the suspension wouldn't even be able to move over its full travel even for a single load, let alone be able to move over its full travel with a variety of loads.

The fact that the total oil displacement of the cylinder is SMALL relative to the total capacity of the sphere for full suspension travel is exactly what makes Citroen suspension so linear, (stiffness vs travel) and what gives it such a wide useful operating load range while still achieving full travel.

No, if a range rover can only travel 8" then 500cc CX sized spheres would be MORE than ample, however the cylinders themselves might need a different length to diameter ratio depending on the mechanical design of the suspension, and you might need a slightly higher system operating pressure (and gas pressure) to cope with the higher average and maximum loads.

Other than that though, it would be quite doable, the only challenge would be physically coupling the suspension cylinders to the suspension arms/axles in a suitable way...

Regards,
Simon

citronut
Posts: 10939
Joined: 29 Apr 2005, 00:46
x 3

Post by citronut » 02 Dec 2005, 20:57

there was a pug 405 gti 16v with hydraulic rear end only aparently it was a production car,i have not seen one though
regards malcolm

rossnunn
Posts: 1254
Joined: 09 Aug 2003, 03:00

Post by rossnunn » 02 Dec 2005, 21:08

Yeh they're about, my Dad used to have one for a couple of months.
citronut wrote: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
Yeh so back on subject, I would have thought the front struts would be a right pain, look how low down the towers are in a Xantia compared to a ZX. You could cut cut out & weld in the towers from a Xantia but then you have a problem with alignment etc.
Another problem with you were going to use Hydractive 3 is the roll bars (in length let alone anything else)

User avatar
fastandfurryous
Posts: 1383
Joined: 07 Jul 2004, 17:57
x 3

Post by fastandfurryous » 03 Dec 2005, 01:16

Mandrake wrote: The displacement in the cylinder is NOT more than the capacity of the sphere, in fact nowhere near it. If we take the 35mm and 70mm figures to be accurate, thats 67cc displacement - compare that to the 500cc capacity of CX front spheres, and thats only 13% of the sphere capacity.
See your point, but.

Imagine this... (and this happens on the rear of my CX)

The suspension is in it's normal ride height. The car is unladen, and the diaphram in the sphere is only displaced by a very small amount. The amount of suspension travel needed (up) to use the volume of LHM in the sphere is less than the total available mechanical travel.

This is noticeable on the CX, as on normal height, it's fairly easy to bounce the back of the car up, and feel the suspension "top out" well before it gets anywhere near the top of the mechanical travel.

That said, I'm sure it would be possible to match the sphere pressure to the suspension cylinder, and allow the full travel of 8" on the front of a Range Rover.

rossnunn
Posts: 1254
Joined: 09 Aug 2003, 03:00

Post by rossnunn » 03 Dec 2005, 02:04

just spoke to my dad, he said it was also a 4x4

jeremy
Posts: 3959
Joined: 20 Oct 2002, 16:00

Post by jeremy » 03 Dec 2005, 02:09

I was actually enjoying the ramblings but to return to the subject - what are you trying to achieve - ultimate speed or unltimate comfort?

You are starting with what I would have thought was one of the best engineered chassis available - regardless of price or type of car and one that will easily handle 150 BHP let alone 72 BHp of the 1.4 engine. It does this quietly , comfortably and reliably which is a further tribute to its designers - which means that to improve it you have to be really good - not just trying something in the hope that it might work.

The old saying that if you want to go faster then there's no substitute for litres still holds good and must really be the way to go and a 16 valve Volcane or Furio has the advantage that its complete with the appropriatebrakes and suspension mods to handle the power.

yes a good BX will ride better and to be honest probably steers better but it won't outcorner a ZX at anytime as it hasn't got the self steering rear axle arangement. A Xantia is a bit bigger and heavier and I think has the self steer rear axle.

So what are you looking for?

rossnunn
Posts: 1254
Joined: 09 Aug 2003, 03:00

Post by rossnunn » 03 Dec 2005, 02:37

Well I'm not planning to go out & do this tomorrow, it was just a could it be done / what work would be involved kinda post.

If I were to look at doing this in a serious light, I'd be looking for a C5 that uses the Hydractive 3 arrangement, for a number of reasons, one is becuase it uses the 'level cornering' of the active but also I think would be much eaiser in the final fit to install as it doesn't use a leaver to control the height, just a couple of buttons. I'd also upgrade the engine without question to one, if not from the same donar car to anything in the Cit range the used the suspension, I'd not dream of running the pump on a 1.4.
The main aspect I was looking at was the fact, if we take the Activa Xantia for example as a Donar car, how good not only does it go but corners too and drop that into a little light / tight chassis like the ZX it 'should' make for one sharp motor with all the benefits that the suspension gives.

As I say, I am not looking into doing this conversion at all, for the time being, it was just a look into what could be done and the workload involved really.

User avatar
Mandrake
Posts: 7790
Joined: 10 Apr 2005, 17:23
x 194

Post by Mandrake » 03 Dec 2005, 05:34

fastandfurryous wrote:
Mandrake wrote: The displacement in the cylinder is NOT more than the capacity of the sphere, in fact nowhere near it. If we take the 35mm and 70mm figures to be accurate, thats 67cc displacement - compare that to the 500cc capacity of CX front spheres, and thats only 13% of the sphere capacity.
See your point, but.

Imagine this... (and this happens on the rear of my CX)

The suspension is in it's normal ride height. The car is unladen, and the diaphram in the sphere is only displaced by a very small amount. The amount of suspension travel needed (up) to use the volume of LHM in the sphere is less than the total available mechanical travel.

This is noticeable on the CX, as on normal height, it's fairly easy to bounce the back of the car up, and feel the suspension "top out" well before it gets anywhere near the top of the mechanical travel.
So you're saying that you can compress the suspension to the mechanical limit, but not lift it to the the mechanical limit in the upwards direction, when unladden ?

Sounds like there is something wrong there, as that shouldn't happen. Most likely the sphere is over gassed.

Too much gas pressure will make the ride softer, but runs the risk of the diaphram bottoming out when the body moves in the upwards direction, when unladden.

Note that an upwards suspension movement translates to a downwards diaphram movement. (Towards the neck of the sphere)

When unladden the diaphram is near the bottom end but should definately not touch during normal operation, as it can cause damage.

You'll find if you put some load in that it won't happen, as now the "set point" of the diaphram for normal ride height will move up further into the sphere....
That said, I'm sure it would be possible to match the sphere pressure to the suspension cylinder, and allow the full travel of 8" on the front of a Range Rover.
Definately, and it should be the same on your CX too...

Regards,
Simon