Hydropneumatic suspension v transverse leaf springs

D

dayofthejackal

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Two of my favourite cars are my 1971 D special and my 1969 Lancia Flavia sedan.

Don't get me wrong I love my hydropneumatic Citroens ( I've got a CX , GSA and an X7 C5 daily driver ) .

How come the good old leaf spring in the Flavia handles even the smallest of potholes so much better than any of the Citroens whilst at the same matching the general ride of its French counterparts ?

My thoughts are that Lancia had been tweaking suspension since the 1920s from its sliding pillar on and got very good at what they did and the physics of Citroen's set up even with added computers doesn't have a sufficient reaction time to deal with sudden changes in road surface .

I would be very interested in the comments / observations of others.
 
How does it go with some load onboard?

The springs might lose their agility.
2cv long soft travel give a great ride, but with a load, which limits travel, they can't match the hydro.
 
hit a speed hump in a cit and there are considerable differences to springs and conventional shocks : )
 
Apart from the mechanical components the benefit of the captured gas in the sphere is the totally progressive nature of the gas spring. Is it Boyle's law ?? Coil springs can be built to offer more progressive action than leaf springs.
The self levelling works because the hydro component functions as a variable length pushrod between spring and articulating arm.
The problem with the sliding pillar designs is the internal stiction. Of course the cost/simplicity balance comes into play too. Transverse springs can offer a dual role. The springing medium and the location and placement of moving suspension components.

https://en.wikipedia.org/wiki/Boyle's_law
 
It's 45 years since i sat in a school science class, but I remember something about pv=nrt
Ok, i remember the p, and the v, and the n, and the t ........ but the r....mmmmm
I'll look it up.....
 
I haven't looked at a Lancia suspension for years, (the springs act as one wishbone I think I remember) but leaf springs are progressive too.
 
All metal devices are elastic within a range, and isn't it defined by Youngs modulus?
E= stress/strain
So any metal spring will be equally progressive, just like gases.
The difference is how you can arrange the elastic elements (length, thickness and direction of stress and strain) to provide the desired travel with the progression matching the intended load range. Then physically package it in a design that suits your application.
A lot of car suspensions gain benefit from the planes of articulation being arranged across the vehicle.
Old rigid axles, with leaf springs mounted on shackles articulated in all sorts of (random) ways.
Transverse leaf springs offer much better (predictable) articulation.
Although some of us love the amazing simplicity of the 2CV, the leading front arms are, in my opinion, not a good arrangement. As any Raider knows, if you drop a wheel into a deep pothole with the brakes on..... the arm will bend!
My 2CV based cars have internally reinforced arms, (Drawings and notes available if anyone is interested) which greatly improve them, but it's still a fundamentally silly design.
I'm planning to replace the entire front end on one of them with a GS subframe.
I will replace the GS hydraulic units with 2CV coil springs with small shock absorbers inside them. Hopefully the elastic range of the springs will be about right.
 
dayofthejackal said:
Two of my favourite cars are my 1971 D special and my 1969 Lancia Flavia sedan.

Don't get me wrong I love my hydropneumatic Citroens ( I've got a CX , GSA and an X7 C5 daily driver ) .

How come the good old leaf spring in the Flavia handles even the smallest of potholes so much better than any of the Citroens whilst at the same matching the general ride of its French counterparts ?

My thoughts are that Lancia had been tweaking suspension since the 1920s from its sliding pillar on and got very good at what they did and the physics of Citroen's set up even with added computers doesn't have a sufficient reaction time to deal with sudden changes in road surface .

I would be very interested in the comments / observations of others.
Click to expand...
The early hydraulic citroens have never been great for small sharp bumps (the CX/GS are slighty better). Simply because there is no rubber in the suspension system to cushion the "thump". The leaf spring car probably has lots of rubber bushes :)

You don't really feel the bump a lot, but you hear the loud "thump"
 
DoubleChevron said:
The early hydraulic citroens have never been great for small sharp bumps (the CX/GS are slighty better). Simply because there is no rubber in the suspension system to cushion the "thump". The leaf spring car probably has lots of rubber bushes :)

You don't really feel the bump a lot, but you hear the loud "thump"
Click to expand...
It's more of a slap isn't it?
 
Buttercup said:
It's more of a slap isn't it?
Click to expand...

Yeah, a short sharp (small) bump can be very loud, and sort of "thumps" through the car. An interesting side effect I imagine of having absolutely no cushioning rubber in the suspension system (the CX and GS have rubber 'bearings" in the lower arms to dampen this slightly).
 
Yeah..... and car companies are still trying to tell us that motoring is more enjoyable with a computer in control.
Forget the computer, fit a carby, points and a clutch pedal...... that's all you need!
 
Buttercup said:
Yeah..... and car companies are still trying to tell us that motoring is more enjoyable with a computer in control.
Forget the computer, fit a carby, points and a clutch pedal...... that's all you need!
Click to expand...

Yeah, well I have a "modern" car now. From 1992. THe newest car I've ever owned. Its a shame I managed to kill it last week :rolleyes: Don't worry, I just hosed the dust off the CX and chucked a battery into it and kept motoring :dance:
 
So who owns the '07 Poogoe - Angie?

It probably has an RHR engine with particulate filter, EOLYS and a truckload of ECUs.

Cheers, Ken
 
Ken W said:
So who owns the '07 Poogoe - Angie?

It probably has an RHR engine with particulate filter, EOLYS and a truckload of ECUs.

Cheers, Ken
Click to expand...
that's boss womens car ..... I've managed to kill the range rover, so I'm back to the CX and ugly pink car at the moment again ..... the 60's and 80's were great times right :dance:

Honestly, the CX probably has more "computers" than the 407 :eek:
 
dayofthejackal said:
Two of my favourite cars are my 1971 D special and my 1969 Lancia Flavia sedan.

Don't get me wrong I love my hydropneumatic Citroens ( I've got a CX , GSA and an X7 C5 daily driver ) .

How come the good old leaf spring in the Flavia handles even the smallest of potholes so much better than any of the Citroens whilst at the same matching the general ride of its French counterparts ?

My thoughts are that Lancia had been tweaking suspension since the 1920s from its sliding pillar on and got very good at what they did and the physics of Citroen's set up even with added computers doesn't have a sufficient reaction time to deal with sudden changes in road surface .

I would be very interested in the comments / observations of others.
Click to expand...
My long departed 1961 Peugeot 403B with transverse leaf front suspension was unbelievably smooth and level on potholed bush tracks. It was also amazing at levelling out the notoriously wavy old Lake George section of the Federal Highway between Collector and Canberra, I still love my C5 X7 wagon though.
 
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