Spheres & roadholding

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Catalin
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Spheres & roadholding

Post by Catalin »

Hi guys,
This is my first post on this forum although some of you may know me form BX Q&A.
This is yet another post on spheres, but completely different from the usual ones.
I need a HARDER suspension for my BX. I own a Series 1 Bx Gt that I use mainly for fun (dashes on curvy mountain roads) and some road racing.
I have 2 suspension setups for my car : the factory one for winter and lower suspension (3-5cm) with « deflated » Bx 16v spheres + thicker rear ARB (22.5mm) for fun. I also use 195/50X15 tyres on Pug 205 Speedlines.
However I am not completely happy with this setup – I need something heavier damped.
I am considering XM Hydractive spheres with these original characteristics :
Front : 400/55/0.7 Part No. 96051826
Rear : 400/30/0.5 Part No. 96051827
Can anyone confirm that these spheres are heavier damped than the Bx 16v ones ? Discs thickness especially.
Any info will be highly appreciated !
Cheers,
Catalin
alan s
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Post by alan s »

Catalin,
G'day mate, Alan here from Oz, good to have you on board. (Took ya long enuf [:D][:D]
Alexx from I think it's Croatia could be the guy to answer this one for you as he is an engineer & has been a revelation on hydraulics & their intricacies since he joined us a little while ago. If he reads this post I'm sure he will contribute something interesting & constructive.
Did you eventually decide on a colour to paint your car? I know a lot are interested to see a photo of the finished result.
Alan S
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Post by alexx »

Well, I think that only source for these information would be manufacturer, since there are no diagrams of sphere damper's characteristics available, only central bore size, which is of marginally importance.
My mechanic showed me different types of spheres when I fitted GS spheres to my BX, but can't remember how thick the discs were on HA spheres.
Anyway, I'm not quite sure you'll get exactly what you want. On conventional dampers, compression-extraction ratio is from 1:2 up to 1:5 (for really stiff racing dampers), while on citroen spheres I think it's close to 1:1, because of "soft springs" (to avoid suspension bottoming). Maybe it's a little higher on hydractive spheres, which can be determined only by dismantling the damper and compare inner and outer discs' thicness.
Since Xantia is havier then BX, extraction damping will probably be high enough for your needs, only the drawback is that compression characteristics will probably be too high, so the ride will be too harsh. Since there are more discs stacked on each side, maybe it's possible to dissamble the damper and move one or two discs from inner to outer side and get wanted characteristics.
That's only theoretically, of course.
If you get some extra info about this subject, keep us posted.
Catalin
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Post by Catalin »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by alans</i>

Catalin,
G'day mate, Alan here from Oz, good to have you on board. (Took ya long enuf [:D][:D]
Did you eventually decide on a colour to paint your car? I know a lot are interested to see a photo of the finished result.
Alan S
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Hello Alan,
I was silently watching this board for some time, minding my own business [;)]
Painting the car proves to be a major pain in the...head [:(]
In my country there are 2 types of MOT. The official one and the "friendly mechanic’s" one. I always go to my friendly mechanic with an envelope and he provides the stamp. Unfortunately, in order to change color I have to renew the MOT, and my mechanic cannot help in these cases.
My car cannot pass the tests as it is modified : bigger wheels, straight through exhaust and large body kit that increases the width of the car.
I have to get approval for these changes and this costs more than the car itself. Still looking for a "connection"
If I can change color, the car will be black with tinted windows.
If I cannot, I’ll try to buy perlescent white although it’s very expensive compaired to high gloss black.
Catalin
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Post by Catalin »

Alexx,
You were right, compression/expansion ratio is 1:1.
Check out http://www.bx.citroen.org/m33/m33.html those Japs really know what they are talking about. No info on Xantia or Xm unfortunately.
I don’t know any way to disassemble a damper from a sphere. As far as I see, it is pressed in place and cannot be taken out. I’ll try to dismantle a broken one
alan s
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Post by alan s »

Catalin,
I'm probably telling you something you already know, but before you start messing around even with a U/S sphere, carefully remove the charging bung from the top of the sphere so as to totally release all pressure.
Even a "flat" sphere can have enough pressure in it to blow your head off.
It just screws out (normal RH thread) but you may need multi grips, vice grips ot stilsons to grab it.
Alan S
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Post by alexx »

Catalin,
thx for that link. Of course, I don't understand Japanese, but there's a fine picture of damper valve, and some numerical data.
It seems that damper valve is pressed into sphere body, and that central bore element is pressed into valve assembly, so you'll have hard work dismantling it.
Since Xantia has stiffer 'springs' than previous hydropneumatic vehicles (HA spheres and also non-HA spheres from '96 on), I presume that compression/expansion ratio may be higher than 1:1, but since the 'springs' are still softer than on conventional vehicles, I don't expect it to be more than 1:2. Unfortunatelly, no data about Xantia on that site.
Anyway, another problem on BX is that, no matter how deflated your spheres are, body roll is the same, since left and right hydraulic cylinders are connected, so you can't get results as good as with conventional springs. It's a different story on hydractive suspension, where there's a crossflow stopper in between.
If you dismantle that sphere, report what's inside. Be careful.
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Post by AndersDK »

Alex & Catalin -
On some of my oldest stock scrap (flat) BX spheres, it appears that the valve should be possible to screw out. This is recognized by the sphere base having an internal threading all the way down to where the valve resides. The valve may certainly be locked by threadlock (Locktite).
I have'nt been researching further on this, but noticed a friend's '94Xantia1.6 did not have internal threading in the spheres. Seems to be a matter of production generation on the spheres.
Catalin
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Post by Catalin »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by alexx</i>


Anyway, another problem on BX is that, no matter how deflated your spheres are, body roll is the same, since left and right hydraulic cylinders are connected, so you can't get results as good as with conventional springs. It's a different story on hydractive suspension, where there's a crossflow stopper in between.
If you dismantle that sphere, report what's inside. Be careful.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Alexx,
For Japanese-English translations use http://babelfish.altavista.com/
it's very good.
Very good point!
Unfortunately I cannot duplicate that ball valve system used in Hydractive, but I can make a sort of damper on the line connecting the struts. A calibrated orrifice should reduce the body roll in tight corners.
I'll keep you posted.
PS. Always concerned for our safety, AlanS! I promise I'll be careful.
alan s
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Post by alan s »

Catalin & Alexx,
When the BXs were being sold out here, a guy raced & actually won a big production race here with one.
I have been chasing him for quite some time to try to get hold of the video of that race which I have been promised. During the race, the many times National Touring car champion was following him in a (Factory) Pug Mi16 & commented on how he could not catch the BX on the corners; he commented "that thing corners flatter than a can of sardines; how do they do that!!??"
It eventually came out that he was using "adjustable" spheres and I hopefully have some of the info on how they did it stored away somewhere as we are in the early stages of preparing/building up a track car ourselves. From memory I'm sure I was told that they removed the dampers & replaced them with ones from a "D" series. They apparently also had some kind of system inside the car whereby they could adjust the pressures in the spheres mid - race if required.
Their efforts were acknowledged by Citroen at the time & much of the technical info gained through experience was taken back to France by Guy Frequilin (sp?) as part of the development package for future competition.
The amazing part to all this was that this was a privateer on a very tight budget, who each time they met head to head, the privateer Cit out did the Factory Pug. So obviously what they did was something special.
If I can find the notes I was given on this, I'll send them across to you as an e-mail.
Cheers,
Alan S
alexx
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Post by alexx »

Catalin,
I found some data for you, stored on my HDD a while ago, so you can compare with BX16V spheres. It's also from a Jpn site (link no longer active) - Xantia VSX corner spheres, models from '96 on:
front: part no. 96238949, 450 cm3, 45 bar, central bore 0.7 mm, bound discs = A2 (0.44 mm), rebound discs = A3+U1 (0.82 mm)
rear: part no. 96238950, 400 cm3, 30 bar, central bore 0.6 mm, bound discs = A2 (0.44 mm), rebound discs = A3 (0.66 mm)
According to that page, 'ordinary' BX spheres have bound and rebound discs = A1+U2 on the front (0.55 mm) and U4 on the rear (0.66 mm). Unfortunately, no data about other sphere types on that page.
If these data are correct, although Xantia is heavier than BX, only low-speed damping of HA2 spheres is significantly higher than on ordinary BX spheres, because of much smaller central bores. Medium and high speed damping is similar (if diameter of main bores is equal - no data about it), only bound/rebound ratio is higher (about 1:2 on the front, 1:1.5 on the rear). So, maybe HA spheres are not stiff enough for you (it's hard to say without trying). But, if it's possible to disassemble and reassemble the damper, you can get what you want combining discs from several BX16V spheres.
So, it seems that in hard mode, suspension of hydractive Xantia is tuned like in other family saloons with conventional suspension - harder springs and higher bound/rebound damping ratio. In soft mode, softer springs and lower low-speed damping is provided by the middle spheres, so Xantia owners can still enjoy the 'magic carpet'.
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Post by alexx »

alan s
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Post by alan s »

Alexx,
How do we convert the "chickens foot prints" to English? Is this possible??
Alan S
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Post by alexx »

I used translator on http://babelfish.altavista.com/ - this link was posted by Catalin. It's not perfect, but it's better than nothing.
Catalin
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Post by Catalin »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by alexx</i>

Catalin,
If these data are correct, although Xantia is heavier than BX, only low-speed damping of HA2 spheres is significantly higher than on ordinary BX spheres, because of much smaller central bores. Medium and high speed damping is similar (if diameter of main bores is equal - no data about it), only bound/rebound ratio is higher (about 1:2 on the front, 1:1.5 on the rear). So, maybe HA spheres are not stiff enough for you (it's hard to say without trying). But, if it's possible to disassemble and reassemble the damper, you can get what you want combining discs from several BX16V spheres.
So, it seems that in hard mode, suspension of hydractive Xantia is tuned like in other family saloons with conventional suspension - harder springs and higher bound/rebound damping ratio. In soft mode, softer springs and lower low-speed damping is provided by the middle spheres, so Xantia owners can still enjoy the 'magic carpet'.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Thank you very much, Alexx. You saved me form unnecessary expenses!
So it’s back to the drawing board [?]
First of all I need to fully understand the suspension basics, then start modifying.
The current setup:
Front: 400/25/1.25
Rear: 400/15/0.7
The “springs” are very hard, only 1-1.5 cm of travel, making the back very bouncy on rough roads and it’s SO easy to lose it.
I think the “springs” should be softer and the bound/rebound = 1/3
What do you think Alexx?
AlanS, please find those notes [:D]
I managed to extract a damper from a sphere without destroying it (the damper I mean).
The sphere is in tiny bits [8] as I cut it in half and pressed the damper out from inside.
It is a rear 16v sphere (pattern, not OE) and has 4 discs on each side. I don’t know the thickness of those discs yet.
At first glance seems to be identical to the one described by the japs. Only the center bore is different, being 0.7mm.
I’ll study it further next weekend.
Cheers,
Catalin
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