Not to start another jacksun topic...

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TB2
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Not to start another jacksun topic...

Post by TB2 »

...but:

I've been watching a lot of "Top Gear" lately and for example I've seen this Zonda F going around their race track. And after seeing the Xantia Activa on youtube, I can't help but feel that all their cars, including the blazing fast Zonda F are just 'wobbling' around the corners. To the left and to the right, in every single corner. Can't describe it in proper English as it isn't my mothers tongue, but the Xantia 'just sits on the pavement flat as a pancake', without any sideway movement.

So: Why exactly is it that pretty much no other car manufacturer uses active hydraulic (or magnetic) suspension on those so called 'super cars'? Why not? I can't really think of any down sides. I mean with such an expensive car, break down coverage or maintenance don't matter at all. And I'm guessing that in all cases a hydraulic suspension must be lighter than a regular spring one, even with 5 liters of LHM, piping and 6-or-so spheres. Or isn't it? What are the reasons that so many cars rely on blunt spring brakes? The cars look so ugly tilting around those corners... No elegance at all. And the price you pay for having a 'race' hard spring suspension on one of those cars is that you feel every single bump. Since I own a BX, every other 'regular' car feels like a brick to me, even as I heard that the BX isn't such a "soft" Citroen at all, compared to a CX or GS. Well...
Carl

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Post by fourwheelsteer »

What I find even sadder is that even the C6 does not use the Activa set-up, at least I'm pretty sure it doesn't.

I'd have a lot more respect for so-called supercars if there was a bit more clever tech under the skin.
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Aerodynamica
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Post by Aerodynamica »

The Xantia Activa suspension is only semi active - or 'reactive' but still the peak of Citroën's suspension system in production.

But back in the late 80s Lotus had trialed fully active systems that used some sort of sensor array that read the surface ahead and then prepared the springs in advance of the bumps and camber - a truly active system. There was also the use of Pito tubes like on an aeroplane.

They used it for some seasons of F1 but additionally, there was a Lotus Esprit S2 prototype fitted with it (I recall watching it on TV's 'Tomorrow's World')

Daft US report on Lotus development


And more daft US reportage


So it's been done! but didn't last (not least due to F1 being shit)

The incredible BOSE system:


My opinion is still in Citroën's favour though as the first semi active system was retrofitted to an ID19 way back in 1961ish - can't find the mad photo though yet. It was not the work of Citroen but a 3rd. party. However, the standard Citroen suspension - for a production car- is still the one that gets MY vote - especially after all these years of success.

I suppose these is some reason other than weight (the BOSE system must weigh a fair bit) that prevents supercars from using it - maybe it's just all about engines......
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Post by Aerodynamica »

Ah! found the ID19 one:


much dutchness to this
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Post by Kitch »

Look, I love the Activa (even with that shite engine) but to even suggest these supercars aren't taking corners as well as a Xantia....it must be April 1st surely? :lol:

Activas can fight roll better than most normal road cars, while retaining a decent ride. They're not setup to stop any form of roll at all costs, which is precisely what a supercar is designed to do.
My daily Saxo VTR rolls less than an Activa in the bends, simply with Billie fast road shocks and Eibach 30mm lowering springs. I have to dodge bumps to prevent damaging my back, but cornering now takes centre stage over ride (not that Saxo's ride well even in standard form).

I'd still say the Activa is one mightly impressive machine. I loved mine and had many moments which in other cars would have been slightly brown trouser!

But reality is if an Activa did their track I'd best it'd come stone dead last. It only has 150bhp, it weighs as much as the Humber bridge and impressive as the suspension is, it's no match for something purpose built to go fast around corners. 205 section tyres aren't wide these days, the front is uber nose heavy, the gearing is all setup for cruising and it'd have to be on amazing tyres to get a decent time for it's class, which of course it would destroy within 6 laps.
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Post by Vanny »

Trying to gain perspective on handling performance from an entertainment show is not the way to do it! Beyond the fact that most aspects of Top Gear are staged, the various super cars going round the track will be going round at 2 to 3x what the Activa could manage. Don't forget that in order to stop the body rolling the inertia has to be supported, in this case it means all the weight is put on the outside tyres (when going round a corner). Look at an Activa going hard round a corner and while the body looks level the tyres are hideously deformed, and right on the brink of loosing all traction, in fact if it wasn't so nose heavy i suspect most Activas would have left the road within weeks of being sold.

As for springs versus hydraulics, its springs every time if you want to do more than 100mph on track. Citroen hydraulic suspension is a hell of a handful, and a tad unpredictable at high speed. Its a lot of fun, but usually slow to react, then all of a sudden very fast to react, then its too late. Look at the various Citroen HP off roaders (such as the BX 4tc and the custom Xantia rally car) and look at the huge numbers of changes made to the hydraulics just to make them work usefully off road.

Then there is the weight issue. For a regular road car, the simple system of the BX is 40%+ heavier than a comparable sprung system. You've got 4 struts, with spheres, various amounts of piping, a hydraulic pump, accumulator, pressure regulator, safety valve, flow distributor, and all the ancillary connectors and union. A regular car has 4 springs and 4 shocks.

Then think about the Activa, struts are 2x at least the weight of those on a BX, 10 spheres, hydractive valves, anti sink valves, computers and electronics, its a huge amount of weight. And compare that to performance road cars, double a-arms, usually super light weight, light weight (magnesium alloy) hubs and carriers, light weight shocks, and typically super short and light springs. You'll find a weight difference i suspect of up to 80%.

I've looked into the pros and cons of hydraulic versus sprung suspension for application to a single seat open racer in a reasonable amount of detail, and there is simply no contest. Springs for the winners.

PS Debating points, rather than ranting!
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Post by Philip Chidlow »

Interesting from my point of view as I am being willingly seduced by Phil 'Kermit's plans for a BX Speed Trials/hillclimb/track thingy based upon a TZD turbo. Having ripped out kg upon kg from the doors, boot, interior and so on (Phil mentioned just how much weight could be shed by merely stripping out the doors and replacing the glass with perspex :lol: ) and having removed the fuel tank and spare/cage maybe making way for a custom-designed diffuser :shock: and so on, it'll be a fairly unique BX, competing as it will in the 1400 petrol modified classes...

How will the suspension hinder or help? Bearing in mind speeds of 100mph aren't necessarily anticipated!
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Post by jonathan_dyane »

That D is amazing, and it leans in to corners too! (The activa doesn't does it?)

I believe Citroen themselves also experimented with semi-active suspension, but not until the early 60s.
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Post by docchevron »

There would of course be the small matter of paying a large fee to Citroen for the use of the hydraulic setup.

As Rolls did.
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Post by Vanny »

And mercedes!
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Post by TB2 »

Of course I was not implying that these super cars would do worse than a Xantia, but rather posed the question if they wouldn't do even better with a hydraulic 'semi-active' suspension rather than springs.

But Vanny and Kitch cleared it up quite well ;)
Didn't expect the hydraulics to weight that much more (given that cars using springs still have PAS and breaking equipment), and the point about the Xantia bending the tyres also makes sense.
Carl

1989 TRD "Entreprise" Turbo Diesel
1989 16 Valve
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- FDV overhaul kit (95.669.034)
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Activa suspension.

Post by citro-geoff »

How about trying a V6 manual chipped Activa in RHD form,(specially built in the UK by BL Auto's in Welwyn Garden City,who also rally an SM!!!)or if you want speed and roadholding,try Neil Hotten's CGAT CX turbo special on the CX forum.All hydraulic suspension in a Mk 1 CX GTi turbo!!!Citroen suspension does work at speed,and without too much change too. I used to be part of a rally team rallying a classic 1962 DS19,and we didn't change anything on the suspension,but wished we had fitted power steering.It started life as an ID19,and was ever so slightly tuned!!!.It is now in the ownership of Malcolm Bobbit,the author and CCC columnist.
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