The DeDion suspension concept is very old: De Dion Suspension | Automotive Terminology Explained

The concept is to have the camber control of a solid rear axle but without the unsprung weight (as the diff is not part of the axle).

Why did they want the above? In the early days independent rear suspension was systems like swing axles and camber control was all over the place and hard to drive, I.e. if you lift off you might end up with positive camber and roll the car.

As far as I know Alfa Romeo first used a DeDion rear axle for their 1950 158/159 Alfetta F1 car which was designed before WWII I believe. Some versions of this car ran with swing axle rear suspension.

I don't know why Alfa used it again for the GTV4/6/Milano. I assume it was cheaper than a proper independent rear suspension. We do have to remember early independent rear suspension for roads cars were systems like semi trailing arms and in BMW's case with I think the 80's 323 caused a tail happy road car that average drivers might find challenging
Pete

 

.....Why did they want the above? In the early days independent rear suspension was systems like swing axles and camber control was all over the place and hard to drive....

The more i read, i see this as a recurring theme at that time. Stability, ease to drive. whether road or race.

I don't know why Alfa used it again for the GTV4/6/Milano. I assume it was cheaper than a proper independent rear suspension.

I wonder about this era in moto/auto vehicle production in UK/europe - you have to assume tooling and manufacturing costs often could have trumped design or performance needs/wants?

I see the system with a blind eye as heavy and overly complicated. But it seems at the time, the weight differences between this and IRS may not have been much if any.
Watts Linkage (or other), Telescoping tubes.. the additional joints, etc etc.

I do see that the Lots 7 (Caterham) utilizes this design, but that vehicle is hardly typical.

 

The way I see it, Alfa knew how to set up properly the rear ends with rigid rear axles. The 105 was critically acclaimed with its well located live rear axle; when the Alfasud came out, it also sported a rigid rear axle, also well located, but a dead one, as it was FWD, and was also critically acclaimed. The Alfetta series followed through with the DeDion as it was still a rigid rear axle, one which allowed the packaging proposition of the rear transaxle.

Why not a fully independent set-up? Maybe they could not get the behavior they wanted from the cars with it. You gotta remember that we love how these cars drive, and most of what you feel from the steering wheel actually comes from how the rear axle behaves. Also, cost might have been an issue, but I'm thinking the DeDion is not substantially cheaper than a full independent setup to make.

 

I see the DeDion as both the best and worst of both worlds. It has the live axle's lack of camber change over suspension travel, but with reduced unsprung weight and no axle windup on braking and acceleration. On the other hand, it has the cost and complexity of an IRS without the benefit of compliance over bumps. Part of what we love (and sometimes hate) about Alfa is how they marched to their own drummer, and in this case, went with the DeDion, while the rest of the world was refining IRS to minimize camber change.

 

Cars used to be designed for their local markets, so German cars tends to tended to have stiffer suspensions to accommodate high speed driving on the Autobahn. They could get away with swing axles and semi-trailing arms in this environment, but produced cars with terrible lift oversteer. Take a look this video from the 1970's of crashes at the Nürburgring for examples. Most of these accidents are due to lift throttle oversteer.

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Italian roads tended to be designed for the tight twisty mountain roads of the peninsula. As such, they needed the suspensions to be more supple than German cars, but retain stability when there were changes in camber. The solution was that most Italian cars until the 1970's had lightweight solid axles that fixed camber but still allowed good ride and handling characteristics. The deDion was a natural extension of this philosophy, and was used on road cars like the Lancia Aurelia earlier. It allowed one to have very soft suspensions in the Alfetta sedans with fixed camber. The design is obsolete now due to multi-link rear suspensions pioneered by Mercedes, but probably was the best mass market suspension design when it came out.

That said, the negatives of the design was that it was expensive and took up alot of space on the car.

Edit: If you go to the seven minute mark, you will see a Junior Z having an incident. It faired much better than most of the other cars, likely because the rear end did not get jacked up in the air.

 

Remember that the alfettas came to market in 74?.. So the design decisions were probably made in 72?… just a wild guess on my part. Then that basic chassis went all the way through to the 75/Milano/es30 in the very early 90’s. ES30 was also the first production car to pull more than 1g laterally. Sure there were other options but in the very late 60’s early 70’s, the end result turned out fairly well. TZ had an irs, but that was an exotic car at the time.

 

Interesting that you mention the TZ, I've always wondered why they didn't productionise that cars rear suspension?

Pete

 

Probably because they struggled with it in period. They were still trying to sort it out when their attention shifted to the GTA programme. Oddly, our measurements indicate that it should be pretty good although it looks like a very complicated setup to productionise.

 

There is at least one RWD car still in production with DeDion. The Smart. So, the concept is not dead yet.

 

I did not know this. Not a lot of length for the arms.

 

The final SZ/RZ dedion cars did have a revised front suspension along with lots of special bits in the transaxle (which find their way into some gtv6 and Milanos today, metal spherical bushes, etc). For sure the lack of funding prevented or delayed engine and chassis development. The Milano was heavily based on type 116 Guilietta! Impressive production numbers for the type 116 cars when you include all the sedans over a 20+ year run. In the 1980s the gtv6 was quite successful in both touring car and rallye competition, before the explosion in technology and funding for the Group B cars and DTM.

 

I had the opportunity a while ago to swap cars with another BBer for a drive on Mulholand. I drove his Alfetta sedan while he drove my Giulia 1300 Super. I was immediately impressed with how the Alfetta maintained grip and sure-footedness with a much more compliant ride than the Giulia.

 

Great video. Esp at 1:05 with the BMW choreography. And also for pointing out suspension travel.
I googled that Smart car and geez it IS a dedion...but that's not a watt link or a panhard rod locating it. In fact to me, it looks as if it should be kinematically locked, which BTW, is what somebody (I think BMW engineer) complained about the 190E 5-link rear suspension. Compliance was thru tuned bushings, everybody uses tuned bushings these days.

 

I googled that Smart car and geez it IS a dedion...but that's not a watt link or a panhard rod locating it. In fact to me, it looks as if it should be kinematically locked, ....

I had to find it as well- here's a photo from the Smart car application

 

It's an interesting rear suspension ... wonder what it feels like if one rear wheel goes through a hollow?

Pete

 

I feel I want an English to American translator here...hollow?? I take it, that it is what in the states, we call potholes.
Which brings up....I believe explicit allowance (and control) of rearward travel of the suspension was being considered, and showing up on cars from the '80s. I think in the dedion setup (and live axles), this will lead to rear steering, as the toe change relative to the body is unavoidable.

 

Sure pothole then. I was being kinder on our road conditions

Pete

 

Super discussion!
I'm 73 and to this day, I have not had a car that I liked as my GTV6. I drove that car daily for 115,000 miles and learned how to drive it real fast, I don't know, probably with a different rear suspension it would have been better in perfomance but never in super frigging exotic looks!!

 

Can you imagine how hard it would be to design a suspension system for a passenger car? You would have so many other people to convince to get your concept to the next stage: Accountants, Production Engineers, Some sort of marketing person who is trying to fit the car in a vehicle category, Sound engineers, Ride engineers ... ??

If you got something through all this it would make sense to have a massive night on the town
Pete

 

I feel a need to clarify 'hard'. The people you mention are involved when it's an economy car. The budget gets bigger (and engineering easier) the further upmarket you go, so we end up with S-classe Mercedes' with Hydro-pneumatics. This doen't explain Citroen, but they're not doing that anymore. I think Rolls Royce also licensed from Citroen in the '80s.

 

I had a Smart Roadster and already then realized the same as Pangolin. The rear axle actually doesn't have motions of freedom. If one would swap bushes for uniballs something would give. But they obviously counted for that and bushes are designed right so it works fine. And the Raodster was handling like a go kart (with the engine size of one as well)

 

I think if you called it a twist beam, I would say....yeah, it kinda is that also, but definitely dedion. That tube looks relatively thin, so I think they actually wanted a little flex, so they didn't use the rear portion as seen on the Alfa. A closed triangle on Alfa vs a C shape on Smart. It also would have added significantly to the space required.

If one would swap bushes for uniballs something would give

Yep

 

As we're on the topic. I have seen the homologation photos of the IRS modified DeDion. Can anyone tell if this was done to lots of cars and which models/series? I think I've seen it connected to GTV6 and/or 75 Turbo.

 

I think it was just the IMSA 75s.

 

The DeDion was the most expensive suspension to build.

Only Alfa and Aston Martin used it back in the day. But Aston didn’t use it that long because of cost.

Alfa and Auto Delta had racing parts to improve handling for those who had money to spend in racing.

 

The 1948 Ferrari 166 F2 had a de Dion rear suspension. I believe most of the Ferrari sports racers thru the 1950s also had the de Dion tube; my father's '55 500 Mondial did. .

 

The DeDion was the most expensive suspension to build.

I could get on a whole long rant, but I think part of what we love about Alfas, at least ones built post-war through 1980s, is that a significant portion of cost was subsidized by the Italian government, so these cars were really bargains as far as content for cost. I don't totally understand all of the politics and culture involved, but the net effect was that the engineers seemed to run things, as opposed to the bean counters. The obvious downside to buyers was that the company was effectively insulated from competition, and so things like build quality, continuous improvement, warrantee costs, etc., took a back seat. But here we all are . . .

 

I feel in some cases there must have been anti-government sentiment, i.e. lets see how expensive we can make this system to spend all their money
Pete

 

PSK, thanks for link to IMSA75. Nice, it has aluminum rear uprights, which are adjustable for camber and toe. I do believe people have achieved this by bending the dedion. Oxy acetylene may be involved, but super crude.

 

Yep, we did that back in the day. Plenty of oxy involved, plus a sacrificial steel wheel with a long steel bar welded across it to act as a lever. But a little toe in plus negative made a huge difference to handling, along with the normal roll centre modifications to sort out the 116 chassis crazy roll axis of course. What you ended up with was a car that could be driven hard onto the apex on a fast corner, a quick lift and then back on the gas. Ah, memories….

 

The DeDion modified for camber I know and they are made aftermarket as well.
I was refering to #5 in this alfa 75 imsa tubolare vs alfa gta cup,, ***....
DeDion cut to make the sides kind of swing axles.

 

a significant portion of cost was subsidized by the Italian government

Well' that's not actually true. The State in Italy (and in other European countries like France, BTW) owns some companies, and many more it used to own. Many of these companies were formally run as any other company, just the Treasury was among the shareholders (or the only shareholder in some cases).

In some periods (when looking for money), the Government was even pushing for dividends, but it's true that usually the State either asked the companies just to have even balances, or pushed significant amounts of money when it was felt it was in the national interest: for instance post-war reconstruction (when the money actually came partially from US) or for steel production plants in the Sixties. Italy low steel production was a historical reason of weakness for Italy. Now everithing is changing, but Italy is still the second producer of steel in Europe (or third, if you consider Russia), so the State actions can't be deemed unsuccessful

Regarding Alfa Romeo, it had even or nearly even balances for a long period. You can find the yearly balances from 1954 to 1985 here: Bilanci Alfa Romeo | Byterfly They are in Italian, but you get the idea.

The truth is that Alfa never recovered from two events: the '73 oil crisis and the Alfasud. The latter was a truly political decision (subsidized, but Alfa had to sign funding contracts).

When the CEO Luraghi asked for money to enlarge the Arese plant to build more Alfettas, that were in high demand, money was refused and instead offered to build part of the Alfettas in Sud plants. He refused, and resigned. This was one of the events that sealed the fate for Alfa.

So, it's true that design at Alfa was more dominated by engineers and less by beancounters, but they manged also to even the balances until the Seventies crises. Whhere money was needed, in the development of new cars, it was often not available. If one realizes the chronical lack of funds for development, and that the last car really designed from scratch was the Giulia (or the Giuietta if one wants to be picky), it looks like a miracle. I think that the perspective should be partially changed: the Alfas weren't extraordinary cars because they were partially paid by Italian tax-payers, they were extraordinary cars in spite of scarce investments. I think ths achivement really needed a commitment from administrators, engineers and workers

Regarding the De Dion, there is a testimony from Giuseppe Busso, variously reported, according which the De Dion was the most expensive and technically best of the three rear suspensions studies proposed for the Alfetta. Probably, I would add, it required less development costs (as opposed to build cost) than a true IRS system, given the experience of Alfa engineers

 

Confused by the statement on the last car developed as the Giulia or 750/101/105 cars. The 116 cars? Perhaps because they carried over the Nord engines? Thanks.

 

@fedegi -- Thank you for better informed commentary on this topic.

 

I think this makes sense now in regards to cost, it's not that the dedion is expensive, it's that Alfa chose a bespoke transmission vs using the existing, as used in 105/115 cars.

 

The deDion is more expensive compared to semi-trailing arms. A semi-trailing arm rear suspension just has two arms attached to the body at an angle. With the deDion, you have the additional cost of welding the bar connecting the two suspension arms, as well as the watts linkage. Note that the Alfa deDion differs from most others in that there is a central pivot point. The Aston Martin used training arm while the Lancia used leak springs.

The Lancia

Edit: Corrected Lancia deDion info.

 

The Aston