[Zinhead]

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.

 

[Zinhead]

The Aston

 

[P-3]

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



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.

No. It was NOT cheaper!!! DeDion suspension was optimum for road cars in that the rear wheels remained perpendicular to the road surface in most attitudes in the suspension travel. Many types of IRS had inherent changes in camber and wheelbase through the arc of suspension travel. The DeDion system proved to offer the most stable suspension in road cars/ sports driving/road racing cars. Front engine rear transaxle afforded a near perfect weight balance and the DeDion suspension offered a smooth predictable handling. The system worked very well in the Lancia B20 coupes.

 

[BryanPhillips]

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. .

 

[pangolin]

I had to google that Lancia monstrosity. I call it a monstrosity, because the 2 hinge points should form a line. Perhaps this gave additional damping. I think the hydraulic tube shock as we know it has not been invented yet.

Rear Suspension - IRS

The early Aurelia had a unique independent rear suspension. Used from the introduction of the car in 1950 through 1953, it contributed to the car's remarkable handling, as noted below: There were...

www.lanciaaurelia.info

and, hmmm, the Aston had inboard brakes too. Did not know that, could have sworn they were outboard.

The reason, I think the Dedion is not expensive, relative to the semi trailing arms, is that it's just a live axle without the differential. So the expense as I see it, is there is a separate diff and half shafts which the semi-trail design has also. And the whole locating that axle has been, and in 60's timing still being developed (I think the Ferrari 250s were live axle on leaf springs), but it's still just stuff they been doing for ages. So the difference is really just the size of the Alfa Dedion with that front triangular structure, and I tend to think that watt linkage as cheap, as it's just 2 straight tubes (except for the GTV6 the had to bend, to clear the exhaust) and a center pivot link. But it is 2 net extra parts.

BMW E30 semi trailing arm. BTW, the Alfa Dedion use the same bearing as the e30. I think it as more complicated then Dedion tube, but I guess machine size to make this is much smaller.

Milano driveshaft in background.

Might as well plug this movie: https://en.wikipedia.org/wiki/Il_Sorpasso

 

[Jim G]

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. .

I was talking about production of regular going street cars. Not limited production street/race cars.

 

[Vivace]

This discussion makes me wonder if a transaxle / De Dion was considered for the Montreal with the added weight up front. Maybe at the time a decision was made that the development cost would be much less by just extending and adapting the 105 chassis. Is all this in a book somewhere?

 

[pangolin]

Edit: Corrected Lancia deDion info

...anyway, I found really good Lancia site, because I was thinking what's with the pivot points ...and wait....Lancia invented the semi trailing arm, then later decided, deDion was better.

 

[Aggie57]

Which were the 3? 1-Live axle, 2-DeDion and? 3-Semi trailing arms or wishbone type..or???


Kinda want to get the 14" steelies now. But I think if I were to do this, I would cut at the current welds, like 300 deg worth, leaving top intact, and then spreading the gap as needed to get the camber I want. Much less heat, and force. But I think it's the front that needs attention, what did you do for the front?

Extended uprights on the front. Joe Beninca did them for us but I’m talking 25 years ago now.

 

[Zinhead]

...anyway, I found really good Lancia site, because I was thinking what's with the pivot points ...and wait....Lancia invented the semi trailing arm, then later decided, deDion was better.

The original Aurelia had an IRS, but the later portion of the run switched to a deDion design. I inadvertently linked to an illustration of the earlier IRS suspension in the original post. The IRS is below.

As a GTV6 owner, it is remarkable how much the Alfetta chassis is an update of the Aurelia design. I would love to drive one some day.

Edit: I was trying to figure out the location of the shock absorbers in this design since there do not appear to be conventional shocks. What is function of the linkage at the rear of the assembly that attaches to the wheel hubs?

 

[Joe Kollmann]

With DeDion, combined with a lightweight watts linkage, the ability to build with considerably less unsprung weight (quicker bounce response, less rotationally shifted mass on accel/decell) is a benefit. Also the geometry in the alfas was such that the roll center of the unit was lower than the top/center ball support setup on the live axle cars. Additionally, reduced changes in camber (which are bad) through the range of greater suspension travel is easier to accomplish. Fewer linkage points means fewer places for the geometry to be displaced under load, with crisper and more reliable response. This made the front and rear roll centers more harmonious as well.
The GTA came similarly to this result, in a heavier and more complex way with the sliding block and watts linkage setups, along with lightened components but it was simpler on the de-dion allowing for the use of elastomer bushings (vs bearings and heim Joints) and hence without the harsh noise and rigid shock transmission of the block and watts systems when implemented on the live axle. Normal humans can drive an Alfa with Dedion fast and well while drivers of IRS cars are most likely to discover the limit more quickly and disastrously. Though few will admit it, especially all those Porsche drivers...In the Porsche pits , talking about snap oversteer is like talking about politics at dinner.

These alfas were among the best handling production cars around. Still well behaved and suitable for unimproved or non-autobahn surfaces. Aston Martin as well as later variants of the Lotus and Caterham 7 used DeDion the latter often described as the best handling car ever, with which I would agree...save the modern, robotically controlled cheaters.

If you're interested in the baseline motivations of different suspension designs (As I am) And want info from a technologically credentialed expert instead of the opinions of us idiots here (few of whom have actually designed a car) take a look at Colin Campbells "The sports car, It's design and performance". Mine is, I think, the 1966 edition. It's answered questions ranging from curiosity as to why a production choice was likely made to how to properly set up the correct geometry on a Panhard rod for a GTV. Your first post suggests an interest in the history and examples thereof so, I think you'd find it at the very least interesting and potentially a lifelong reference guide as I have. It sits directly adjacent to Piero Taruffi's Technique of motor racing which is similarly dog-eared and loved. Both are still in print to this day. These references are significantly dated having been written in the 50's and 60's but not all that much has changed and they make great references for vintage designs. If you read and understand these you will be here, observing the uninformed and ignorantly speculative opinions of the masses as entertainment rather than reliable resource.

 

[PSk]

The original Aurelia had an IRS, but the later portion of the run switched to a deDion design. I inadvertently linked to an illustration of the earlier IRS suspension in the original post. The IRS is below.

As a GTV6 owner, it is remarkable how much the Alfetta chassis is an update of the Aurelia design. I would love to drive one some day.


View attachment 1773328

Edit: I was trying to figure out the location of the shock absorbers in this design since there do not appear to be conventional shocks. What is function of the linkage at the rear of the assembly that attaches to the wheel hubs?

Lever arm shock absorbers such as used on MGBs way too long and were the thing until telescopic shock absorbers were invented.

I don't see the Aurelia influence as much as you do. DeDion sideways location is panhard versus watts linkage. Leaf springs versus coil, and leaf spring for axle location versus the strange central pivot for the GTV6.

But they are cars designed for the same purpose and position in the market.

in the end there are only so many ways we can design a cars suspension ...
Pete

 

[pangolin]

I see the influence as the transaxle with inboard brakes. The rest is just like live axle dominated US car production from 60s to 70s, the transition from leaf springs to coil springs.

 

[Joe Kollmann]

Almost forgot, for the OP, Lotus 58 formula 2 car. Front AND rear DeDion.
And just for good measure, the 375 and 250 TR Ferraris and 5300 Bizarrini Stradas and Iso Grifos used it too.

Certainly not for lack of funds to use a "proper" IRS.

 

[PSk]

I see the influence as the transaxle with inboard brakes. The rest is just like live axle dominated US car production from 60s to 70s, the transition from leaf springs to coil springs.

Who influenced who ... Alfa 8c2900 had a transaxle and independent rear suspension
Pete

 

[Zinhead]

Who influenced who ... Alfa 8c2900 had a transaxle and independent rear suspension
Pete

And the 159 Alfetta had a transaxle and deDion rear suspension but it was not a road car.

Lever arm shock absorbers such as used on MGBs way too long and were the thing until telescopic shock absorbers were invented.

I don't see the Aurelia influence as much as you do. DeDion sideways location is panhard versus watts linkage. Leaf springs versus coil, and leaf spring for axle location versus the strange central pivot for the GTV6.

But they are cars designed for the same purpose and position in the market.

in the end there are only so many ways we can design a cars suspension ...
Pete

I totally see the influence. Transaxle, deDion, inboard brakes, 60 degree V-6 in a chassis that accommodated a wide variety of body styles. Both the Aurelia and Alfetta chassis were designed to excel at everyday driving, and they both had world class handling for their time.

 

[pangolin]

Extended uprights on the front

How did front behavior change?

 

[guimurad]

Almost forgot, for the OP, Lotus 58 formula 2 car. Front AND rear DeDion.
And just for good measure, the 375 and 250 TR Ferraris and 5300 Bizarrini Stradas and Iso Grifos used it too.

Certainly not for lack of funds to use a "proper" IRS.

millers also used DeDions on FWD and 4WD cars

 

[Aggie57]

How did front behavior change?

in combination with lowering the rear roll centre - via a lowered watts linkage center pivot - it pretty much removes the outside front ‘kneel’ inherent in 116 cars. To the extent that we ran without a front sway/roll bar which goes against the approach many take.

But there were many other small tweaks as well, like a stiffer adjustable rear sway/roll bar.

 

[pangolin]

I feel you really mean inside (the less loaded tire is on the inside of the corner) kneel. I feel every time I see a 60's vintage US car, that inside front has way too much negative camber with respect to the car, and it really needs to camber outward. Yes, I think Alfa DeDion cars probably could use a bit of de-cambering.
I think this screen grab is of Australian origin.