The mastery of Hydrolastic suspension

One of the most innovative suspension designs ever. Variable spring rate, variable damping rate and front/rear interconnected to reduce pitch. And it was fitted to millions of cars!
Buy my book on the history of car suspension here - www.amazon.com/Car-Suspension... (or from Amazon in your country)

[@sicko_the_ew]

I had a Citroen GS from late 70's/ early 80's when I was young. I got too inquisitive about what was going on inside it, pulling things apart, and then having a tin of mystery bolts left over on reassembly. As it turns out, one of those bolts kept a hydraulic pipe from rubbing on the exhaust pipe, and I had a lucky escape with it. Drove down a very steep hill (with drop-offs in places, where if you went through the barriers, you'd fly far enough to achieve certain death), parked, and tried to start in the morning. It wouldn't rise up. So I looked and found the hole where all the hydraulic fluid was escaping. The reason this was a lucky escape is that the Citroen's brakes were part of the suspension system! If that pipe had worn through just 20 km earlier (instead of doing so very soon before I got into my parking), I could've easily died or killed someone. When it worked, it was fantastic. You could hit the tops of ridges or bumps in the road that sent the car flying through the air for a while, and when it hit the gravel/ tar again, it was perfectly sure-footed. (A stupid kid who pulls things apart out of idle curiosity and also had a reckless streak drove that car. Idiot. Hard to believe it was sensible me.) Best thing about it was that it sank right down to the ground when you parked, and then when you started up it would first pick up its bum, then its front. Always entertaining to start up in front of rural Zulus (for me and for them). Other people probably also thought it was strange, but most people are not very open in reacting to something like that, and don't smile as readily as they might, so the reactions I remember are the laughs or grins of Zulus who know how to appreciate a bit of magic.

[@russkisteel]

you would have had a plenty of fluid before completely running out of it so unable to brake. i should know because my xm hydraulics failed, it took a few minutes to lose all fluid from high pressure side. it doesnt take much fluid to brake unless completely dry and you'll know about it well before getting to that. i always hated sinker citroen because it takes a bit of time to pump up to normal height.

[@sicko_the_ew]

@@russkisteel OK, so while driving, there might've already been some fluid loss (but I don't recall feeling it - but it was a long, long time ago). And then when I started up, instead of rising up it was just pumping fluid out while I waited, I suppose. The hole in the the pipe was quite big, so would've grown to that size as I drove. (I suppose when it went, the thinner metal went easily. Some lubrication might've sped up the grinding. Whatever it was, it was quite a leak. I didn't mind the sinking. (Sometimes it was quite fun, as above.) It was a very "sure-footed" car.

[@peterriggall8409]

Great video. I have just purchased a 1970 Austin 3 litre. One of only 6 in Australia. Always been interested in the Hydrolastic system and enjoying learning more about its application in the 3 litre. Great explanation.

[@JulianEdgar]

Yes a local to me (in Canberra) has one that I occasionally see at car shows. Always wondered what it would be like on the road!

[@lawrencewillard6370]

Had a Austin 1800, very good suspension, easy to replace, as I found out. Only replaced it when it got older. A front unit collapsed, to be found in the morning. Replaced it myself, easily. Utilised the clutch unit to pump fluid to restore ride height. Worked for years.

[@cabletie69]

nice adaptation.

[@lawrencewillard6370]

@@cabletie69 Necessity. Had access to other vehicles to chase for parts. My job required innovation, so a good start. Children could play on the floor in the back, so much room. This was in the mid 80s.

[@jeremyrichards8327]

My father had a Mk 1 Austin 1800 and my 3 older brothers drove it on holiday in Devon.Loads of room, good servo brakes and smooth 5 bearing B series engine. Also later a MK2 Austin 1800S which was less refined but quite fast for the time.

[@Matteo_Licata]

Hi Julian, I bought and read two of your books, and I appreciate very much your work. Something that surprised me in your excellent book about suspensions is the absence of Lancia's "Sliding Pillar" design, used on the Lambda and most subsequent Lancias until the last Appia was made. Will you ever make a video about it? Thank you!

[@JulianEdgar]

The videos are done only to promote the books, so I don't cover in videos any topics not covered in my books. I'll add the Lancia design to the list to be considered if I do a second edition.

[@pedromiguelareias]

And... still used in Morgan cars

[@doneB830]

I had a workshop in England in the 90s so there was still a lot of older ones around and the metro. They drive very well and I was surprised how reliable they were compared to any other suspensions systems. I like it.

[@UPnDOWN]

I ventured over from the Citroen hydropneumatic side of things, and found that really interesting, thanks! I should probably get a Metro while I still can! I remember having a go in one and remarking what fun it was around corners.

[@mauriceupp9381]

I love these kind of things when I was a kid I used to draw this stuff up and I didn't know anything about car suspension

[@mauriceupp9381]

I bet that would work real good on those four wheelers they go out and run around in the woods with

[@moodyyuhoody]

I have a Morris 1100 and the ride is quality. It is a joy to drive and I often find myself smiling like a loon as I throw it into corners

[@dreamdiction]

This is the best video discussion of hydrolastic suspension. 15:30 I agree that the Austin engines were noise and harsh, but why? What made them like this?

[@arrindaley3714]

Thanks for the video, I'd add longevity to the list of advantages, given the displacers haven't been made for possibly half a century but there's still Hydrolastic cars driving today, most I'd guess on thier original displacers, then they seem to get replaced because of hose failure not the displacers themselves. How many conventional suspensions have lasted 50 to 60 years without shocks or new springs?

[@simonlinser8286]

great video thanks

[@indopleaser]

thank you, so hard to find a video with new knowledge

[@JulianEdgar]

Glad you enjoyed it!

[@gafrers]

Brilliant

[@billybobhobnob101]

Fantastic video, I had know a little about this type of suspension and it sounded very good but I thought it must had some type of problem otherwise it would still be used - sad to see maybe just a lack of imagination/ or at least a fear of going off the most tread path- I'd explore this if I was one of the many new electric car start-ups, in fact it would fit right in with my dream of a very mechanically simple retro electric car.

[@rickehrlich5823]

No other car maker has chosen to adopt hydrolastic or hydra-gas.

[@ShawnD1027]

I can see how the units could be bled when vertical, but how were they bled when horizontal? It'd seem that air would be trapped above the pipe connection.

[@JulianEdgar]

The system was evacuated with a pump prior to the fluid being added.

[@ShawnD1027]

@@JulianEdgar, that makes sense. Probably something most DIYers wouldn't have on hand.

[@JulianEdgar]

Back in the day people used a modified grease gun as the pump, I think.

[@colingarner6175]

I think there might be confusion here , hydrolastic is the cheap suspension that British Leyland used but it’s not the system that Citroen developed which was Hydropneumatic.

[@JulianEdgar]

What is the confusion? Both systems are covered in my book - their respective advantages... and disadvantages.

[@pjay3028]

Oh, I wish I'd known this detail when I owned my Allegro, I'd have appreciated it so much more.

[@cliveclapham6451]

Hydro gas on Allegros 👍

[@pjay3028]

@@cliveclapham6451 yes, but as mentioned in the video, the fundamental principles and advantages are basically the same, just swapping rubber for gas springs. So even more to appreciate!

[@cliveclapham6451]

@@pjay3028 👍👍👍

[@shinequashie393]

You absolutely need to analyze the Aptera vehicle

[@AndrewShingange]

I'm not sure quite where I missed it if at all but what are the disadvantages of this system, if any? Why is this system not in use in modern cars? It seems genius!!

[@JulianEdgar]

Disadvantages include ground level roll centre and front castor change with deflection. The system best suits narrow tyres.

[@timcarpenter2441]

​@@JulianEdgar Surely this is an issue with a particular geometry. Hydrolastic is not dependent on that

[@timcarpenter2441]

One issue was not coping with heavy rear loads, as the compression at the rear caused the front to rise, exacerbating the problem. I am sure it can be resolved today.

[@JeredtheShy]

Funny I don’t see any powerful springs under tension that you’ve got to handle carefully or they can kill you. Why didn’t this become a much more common arrangement?

[@Iowa599]

The pressures in a suspension displacer unit (aka: spring) are under the same load as springs when the car is on the ground. Granted, when the car is off the ground the pressure does drop to zero, but so do steel springs with zero (or less) preload.

[@bobdoingbobthings]

Does your book cover the suspension system on the McLaren 720s?

[@JulianEdgar]

No.

[@DavidUKesb]

Hello. On my ADO16 the both rears sit just slightly too low, one front is about right and the other front is slightly too high. If the front and rear are connected on one side I can't quite understand how this would be the case. Any thoughts would be much appreciated. PS Is it possible to pump up a hydrolastic suspension with a hydrogas pump? Many thanks.

[@douglaspage1085]

I'm testing a selection of displacers by pressurizing them displacing them a fixed distance and noting the change in pressure. On a mini would you put the softer ones on the front to control pitch or the stiffer ones due to the heavier front?

[@JulianEdgar]

If they are normally the same front and back, I'd put the stiffer ones at the back to improve handling.

[@tedpalmer5552]

Did the original Hydrolastic have too much roll resistance? If I recall correctly the aussie Austin Tasman/Kimberley had the displacers connected diagonally.

[@JulianEdgar]

No these cars did not have diagonal displacer connection.

[@FentoZ]

Would be great if you could do a video on the lordstown Endurance aerodynamics

[@JulianEdgar]

No detailed tech data available is there?

[@FentoZ]

@@JulianEdgar no, vut would be nice if you made a speculative comparison about all the upcoming ev trucks, cybertruck,rivian,ford ev f150,endurance, just by yhe visuals, since you are good at it, I know very likely cybertruck has the lowest drag, folowed by maybe the Endruance ,,

[@JulianEdgar]

@@FentoZ Sorry. I think guesswork is pointless. In fact worse than pointless because it is usually misleading.

[@julianleyton8668]

Great to see you on hereJulian.. I used to follow your brilliant series (Autospeed ? - sorry I’ve forgotten the name) and even as an engineer myself I’ve never read such subjects with as much interest as I did yours. You explained everything so clearly yet comprehensively. I suspect Hydrlastic was not adopted by others for one reason - cost. Although I was a big fan of Hydrolastic and Hydragas cars (owned and drove numerous) I can’t help but think that a coil spring would be much cheaper than the BL displaced units.

[@JulianEdgar]

An SAE paper prepared by Moulton shows that when the whole suspension (not just the springs) was taken into account, it was marginally cheaper than conventional suspension.

[@julianleyton8668]

@@JulianEdgar As referenced earlier, I have massive respect for you, your knowledge and explanations. I am a big Hydrolastic and Hydragas fan and I have worked with both systems for many years, however, find it almost impossible to believe that the displacer cost a similar amount to a simple coil spring. The mechanical elements of the two suspensions systems are very similar, or could easily be designed to be thus. Surely it is no coincidence that the report you mention was prepared by Moulton !

[@JulianEdgar]

@@julianleyton8668 It was Hydragas - Allegro front suspension versus Volkswagen Golf. Hydragas 94 per cent of the weight and 96 per cent of the cost. SAE 790374. Hydragas needed no fine machining, sliding seals, chrome plated rod etc as normal struts do. It's not just the spring.

[@SuperFunkmachine]

@@JulianEdgar Once you have a big factory to make the displacers, but every one else had piles of coil springs and gas shocks and was set up to make them.

[@sestar111]

Hello Julian,, I would like to ask you what is the difference in fluidity between hydrolastic and hydrogas? How do you fill that Hydrogas? With what?Is it not that some gas is injected inside the shock absorbers? I had an Allegro 1.3 and I had a lot of problems with those shock absorbers. I can't change them because they weren't on sale, so I had to sell the car. Now I feel very guilty for doing that, but I still don't know where I went wrong? So, I had an improvised pump, without a potentiometer, of course, I used the bias system from the Austin 1.3 on the stand, so that I would have something to fill hydrolastic, or hydrogas, whatever it is. I put antifreeze in the system, 70% and one 300 mlg of medical alcohol of 100%, and with that I filled and topped up the shock absorbers. But....as I can see and as it turned out - something was not right..The ride was very stiff, just like if you were driving a /mini', it bounced car, it was not soft at all, even though it was 35-36 cm from the middle strap to the edge of the wing. Where did I actually go wrong? Please answer me, because if I found it here somewhere in Macedonia, I would buy it again, because had a phenomenal engine and an even stronger body. thank you very much and greetings from Macedonia.

[@jamesengland7461]

Excellent video! Why, do you suppose, is this genius suspension not practically universal?

[@JulianEdgar]

I think that suspension engineers have largely lost their way in terms of innovation, especially on low cost cars. It's all now just trivial variations on the same themes.

[@rossjuniper3610]

Hi Julian, i have a question that i cant find anaswered in your videos. How can i contact you to ask about this? May make an interesting video for viewers too.

[@JulianEdgar]

My email address is under the 'about' tab (accessible from a PC not a phone, I think)

[@maxspruit8370]

Wasnt there a problem with the rubber creeping/gradually changing shape over the years? For example: i just found that my egine sits so low that sometimes it contacts the chasis. This is because te rubber in the mounts has become thinner/has crept over the years. Would you expect the same from these kind of springs.

[@JulianEdgar]

The original tech papers goes into creep in great detail. Basically, the car was adjusted in height before each car was sold and then it was fine - and if not, it could easily be adjusted in height at any service (just add some fluid).

[@maxspruit8370]

@@JulianEdgar, Awesome, forgot about the adjustable fluid pressure. I'm allways really impressed at the novelty of the information you offer. It is very impressive.

[@compu85]

Cool springs sag over time too!

[@madcockney]

@@JulianEdgar Service Centres and garages at the time often advertised that adjustment of the HE suspension was included. This was also stated for the later gas version.

[@ProtonFilms_Mark]

I wonder why there isn’t an aftermarket kit like this. I realise that with the lever ratio like that, the chassis probably has to be designed around them, but the premiere reason must probably be an uncomfortable ride is easier to sell to the “performance”-oriented driver. What happens if all four wheels are compressed? Better yet, can a similar solution be implemented to a modern car with 4 macpherson struts (for the sake of simplicity) and adding a hydraulic cylinder to each corner at the same approximate 1:4 ratio you demonstrated in the video, connected front to rear in the same way? Would that produce any result at all for that matter?

[@JulianEdgar]

The nearest is air suspension, which Is why I went with a full custom air suspension in one of my cars. Covered in my book - www.amazon.com/Custom-Air-Suspension-suspension-SpeedPro/dp/1787111792

[@JulianEdgar]

If all four wheels are compressed, the suspension is firm. Same as if two wheels on one side are compressed - roll stiffness is greater than one-wheel bump stiffness (which is what you want - nothing serendipitous about this suspension).

[@ProtonFilms_Mark]

@@JulianEdgar all in all brilliant system, shame it wasn’t widely adopted.

[@alancrossley509]

Hi Julian. I live in South Africa and have a caramel brown Austin Apache TC with a vinyl top which has the hydrolastic suspension system, which after standing for a good few years, has collapsed. Apparently the system is a sealed system which to my reasoning would mean that there is no way to pump new fluid into the system. I presume that it somehow developed a leak and subsequently "deflated". Unfortunately there is very little information pertaining to or regarding the servicing of the hydrolastic system online. I found one diagram online which does not seem to show a bleed nipple but merely states that it does not require any maintenance and that "the fluid in the system is in for life" any advice would be most helpful.

[@JulianEdgar]

Fluid can be pumped into the system to raise the car again. The factory Hydrolastic pumps are now rare but a grease gun or similar can be adapted for use. Contact one of the clubs in the UK that specialise in Austin.

[@alancrossley509]

@@JulianEdgar Thank you for your prompt reply!. That is good to know ...I shall be i touch with an Austin car club as suggested. Very well presented and informative I learnt a lot from your video. Thank you.

[@kevinbarry71]

Looks like a great system; why do you suppose it is no longer in production anywhere?

[@JulianEdgar]

My gut feeling is unimaginative, risk-averse car companies - and of course, modern car suspension engineers who have no idea the system even existed, let alone any understanding of its sophistication!

[@TC-V8]

I worked at Rover when they changed the Hydrogas MGF to conventional sprung MGTF and I'm afraid the main driver was cost and saving money. Secondary was hydrogas would slowly leak meaning your MGF suspension would need routine maintenance (pumping up) to maintain correct/safe ride height.

[@budisutanto5987]

My opinion : planned failures. Jack up spare parts sells. Every bump cause annoying sounds, makes people wants to buy new car. Automatic Emergency Braking System isn't a new invention. But only available on the highest, most expensive type. One of the reason internal - combustion - engine car downfall : safety. While in Tesla car, it's not an option : build in AEBS. You don't think that technology suddenly at Self driving car, did you? You might want to see a real life base movie : Tucker, a man & his dream. -> corruption, back stabing in car industry. People safety isn't their concern. Greed.

[@rmariu]

I only remember a bouncy ride and not a magic carpet ride. Never tried the hydrogas versions. Were they better?

[@JulianEdgar]

What is a bouncy ride?

[@cabletie69]

bouncy = heaving?

[@rmariu]

@@JulianEdgar It felt like I was always moving up and down with a small amplitude. It was a Morris 1100 in the 90's. Not exactly fresh off the showroom floor. I do remember standing on the tow bar of an Austin 3 litre and jumping up and down. (Again in the 90's) and it seemed if the tires flexed more than the suspension.

[@JulianEdgar]

Yes all of the Hydrolastic cars I've experienced have had fairly firm suspension - certainly not floaty.

[@rmariu]

@@JulianEdgar Firm yes. I would not use the word supple. kzbin.info/www/bejne/rZbUhmyEr6ybd9U

[@olivialambert4124]

I see a fundamental problem fitting it to modern cars. Namely that the Macpherson strut is so important for so many modern cars, both for space and cost. I don't see a reasonable way to make this work with the Macpherson strut due to both the demand for a strut rigid against lateral movement, possible but would require a number of extra parts to create a sliding pillar for said strut, and due to lack of any leverage ratio. Again possible, but then you're starting to add a bell crank making it more expensive, even less space efficient, and really you're making a mess of the whole thing.

[@JulianEdgar]

That presupposes that MacPherson struts are a requirement in suspension.

[@olivialambert4124]

@@JulianEdgar Thats exactly the point. Modern cars are sacrificing so much already to fit the tightest engine bay possible. Engines have shifted towards I4 or V6 as the largest, the perfect inline 6 is gone. Designers are happy to deliver torque steer for a smaller engine bay, looking for alternative solutions. Turbos, LSDs, everything has been stuffed into the already tiny bay with no extra space. A space critical suspension setup is more important today than ever before, and the designs demonstrate even a decade or two ago it was near essential. I really don't think its about the cost savings of a MacPherson strut anymore, for which it was originally developed. When designers are rushing en mass to put semi active dampers on a MacPherson strut and almost nobody is using anything else (in the markets which might consider hydrolastic) I really can't think of another conclusion to make. And as cool as Hydrolastic is, I just can't think of any realistic way to modify it to a similar footprint up front. Without a paradigm shift, the closest I can reasonably imagine is the hydraulic FRIC put onto exotic cars becoming more common, though fully active electronic might see that entirely go soon too.

[@JulianEdgar]

Thanks for the detailed response. Since ICE cars are likely to effectively disappear in the next few years, I don't think future packaging constraints re front suspension will be much like they are today. And with electric drivelines having less clear product differentiation than ICE engines, I think the time is ripe for electric vehicle manufacturers to add ride comfort back into the arsenal of competitive advantage. A modern approach to Hydrolastic, with its low pitch, inbuilt variable damping (but probably using air springs rather than rubber) could be low in cost and highly effective.

[@olivialambert4124]

@@JulianEdgar Whilst I don't think ICE cars are going to disappear for quite some time, it does bring up some interesting points. So firstly the price, the copper commodities market, the electric infrastructure, and the general physics around electric cars all really prevent electric from becoming the predominant form of engine for perhaps the next 20+ years. I would anticipate within the next 15 years or so (well after the deadline for EU nations) that a hybrid car, small batteries and electric motor, very small ICE engine, to take over. Something like a 600cc or smaller motorbike engine (maybe 2 stroke), though the EU mandates have really pushed that back somewhat. Indeed from my understanding car companies are already testing with a similar setup. With such a setup I'd anticipate engine bays to get significantly smaller, though the tradeoffs would likely allow more space for suspension if the benefits are there. However the price of semi active dampers and other electronic suspension systems have fallen rapidly in the past few years and only seems set to continue. I can't envisage many cars in the next decade from having at electronically aided suspension. Given that, such a system could emulate hydrolastic an other FRIC systems reasonably well without the interconnectivity whilst giving many other benefits too. In higher priced cars I would anticipate fully active suspension to take over, though there certainly is a window for FRIC systems to thrive - perhaps a decade or so. Indeed they do have a lot of developments over the past decade and FRIC is gaining more traction in the sporting world, but they usually tend to be a conventional coilover suspension setup with hydraulics (or mechanical linkages) added rather than the clever hydrolastic system where everything plays multiple roles in the design. So double wishbone, multilink or MacPherson with coilovers and FRIC seems the most likely there. But I do agree suspension comfort is a very real avenue of improvement for even the budget cars, frankly I agree they should have been focusing on it far more for a while now. And like you I do hope FRIC becomes more mainstream. But for hydrolastic itself I see the window closed in about the 2000s, though I think they absolutely should have been regularly using it up to that point.

[@leoarc1061]

So, what's the catch? Reliability? Cost of maintenance?

[@JulianEdgar]

No catch that I am aware of.

[@leoarc1061]

@@JulianEdgar I've been thinking about this suspension layout. Perhaps the reason why it wasn't widely adopted was due to the fact that it tends to raise the roof line, thus increasing frontal area. Now, with electric cars, I think such layout should be given another try, as the battery tends to sit on the floor of the vehicle, so there should not be an increase in frontal area. I would love to hear your thoughts on this matter. Many thanks.

[@JulianEdgar]

@@leoarc1061 (1) Why does Hydrolastic raise the roofline? (2) How does the position of the battery in an electric car make any difference to frontal area?

[@leoarc1061]

@@JulianEdgar I must apologize. I made a massive mistake. I thought that I was commenting on your Citroen 2CV video and its suspension. There's absolutely no reason why hydrolastic suspension should raise the roofline. Battery powered cars tend to have the battery on the floor of the vehicle, which, everything else being equal, will raise the roofline when compared to a similar FWD ICE car. There would, therefor, be space to implement a 2CV-style horizontal suspension with few compromises. But we are not talking about that here. The video is about hydrolastic suspension, not the 2CV. My apologies. I need to be more attentive in the future.

[@tiitsaul9036]

Thanks for for sharing. Why car industry didn’t pick it up?

[@JulianEdgar]

I think that suspension engineers have largely lost their way in terms of innovation, especially on low cost cars. It's all now just trivial variations on the same themes.

[@madcockney]

@@JulianEdgar In the UK there were quite a few complaints about the Hydroelastic suspension at the time. I have driven quite a few of those cars from around the 60's and early 70's that friends or family owned but never owned one so no long term experience. IIRC one of the issues was road holding, good in a straight line but otherwise inferior. However most cars wallowed in those days which is not something we would want today, so what part of the issue was the suspension and which part was due to vehicle construction is an unknown to me. In those days a motorcycle could get around a given corner faster than a car, which is the other way around today. (I am not encouraging people to drive or ride too fast around corners on the road even if it is possible due to hazards and the safety of others.)

[@JulianEdgar]

@@madcockney In fact, if you go back and read the original motoring tests of the time, you'll find that Hydrolastic was universally praised for both ride and handling.

[@SuperFunkmachine]

@@madcockney The amount of tolerance in the frame and suspension mounting points was huge, 20mm +. Add in the low bend and torsional rigidity.

[@rickehrlich5823]

@@madcockney hydrolastic was not only the best ride ever it offered wonderful road handling even on curves. As mentioned the displacers stiffened up under load. There was body lean but it was controlled and presented no difficulties.

[@ScaniaFung]

is MGTF use this system?

[@JulianEdgar]

MGTF uses Hydragas. Similar.

[@ScaniaFung]

@@JulianEdgar Hydrolastic is hydro only, no gas?

[@JulianEdgar]

@@ScaniaFung Covered in the video. Hydrolastic uses rubber springing.

[@bilaltariq7819]

There have been some FSAE cars that have taken this further: kzbin.info/www/bejne/janXl2CCecece68 and the UWA 2005 FSAE car

[@JulianEdgar]

Completely different system isn't it? www.fsae.com/forums/archive/index.php/t-8097.html?s=5ce42bd67e1ff12ad0ef134603742939

[@bilaltariq7819]

@@JulianEdgar I meant in terms of connected suspensions, in the video I sent they control each wheel with a hydraulic actuator and have a control unit that connects all the wheels together and controls each mode separately.