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It's a de dion suspension, which is kind of in-between a swing axle and IRS.  Think of a live axle configuration (sort of) that acts like an IRS to the extent it allows the rear wheel camber to stay constant during bump and roll.

To my knowledge, if you wanted an "IRS" from either SE or V, this is how they've been doing it, because it can be configured to their existing chassis (although I think both are developing chassis redesigns to allow for more familiar configurations of IRS).

Yes we did about a dozen cars with this suspension and it was more for the purpose of the specific engine fitment and less for the suspension (they used an inline 4 VW flex fuel motor at first and later an Audi TT motor) mated to a VW/Audi 5 speed box. Several were later converted to Subaru, upon request.

It had its pros and cons, but in the end it just didn't handle as well as a properly set up swingaxle (not many do) and the trend was going way more Subaru than anything else, so it made sense to do them with the stock chassis and VW transaxle beefed up a ton.

Handling: in a straight line it was very civil and felt great.  Mildly aggressive driving it also did great, but when you really pushed it it just wasn't as good and had a violent "snap" point where there was no coming back from it... hold on and try not to get dizzy.  :-)

@edsnova posted:

Your car had one @RS-60 mark did it not?

@DannyP posted:

No, Mark had IRS that he designed and built.

I built a 5-link IRS.  I went this way because I didn't really know for sure exactly where I would need the rear tires to be planted once I started mounting the body.

Basically, the build was conceived by marking four dots on the floor where I thought the wheelbase should be, and then to build a car that would fit those four dots.  I thought at the time it was pretty ambitious (or naive) to believe that those dots would really hold up true through the project.  So when it came time to think about rear suspension it evolved that a 5-link would provide some reasonable flexibility to adjust wheelbase (shorter or longer), track (in or out), plus whatever I wanted for camber and toe.

Since I really didn't know what I was doing, I shopped around for ideas.  I ended up looking at the rear of a Lotus 49 and figured there's a guy that probably does know what he's doing; so, I (sort of) copied it.

Of course, if you copy a race car suspension it will probably end up riding down the road like a race car, which it does.  All your rear suspension connections (18 of them) are unforgiving, hard, no cushion heims.  So, when the road surface is not smooth, the harsh ride can get weary after a while.  On the other hand, when the road is smooth: 

@RS-60 mark posted:

Of course, if you copy a race car suspension it will probably end up riding down the road like a race car, which it does.  All your rear suspension connections (18 of them) are unforgiving, hard, no cushion heims.  So, when the road surface is not smooth, the harsh ride can get weary after a while.  On the other hand, when the road is smooth: 

Or, if you're driving the car the way it was meant to be driven. At that point, you just don't care about harshness!

@chines1 posted:

Yes we did about a dozen cars with this suspension and it was more for the purpose of the specific engine fitment and less for the suspension (they used an inline 4 VW flex fuel motor at first and later an Audi TT motor) mated to a VW/Audi 5 speed box. Several were later converted to Subaru, upon request.

It had its pros and cons, but in the end it just didn't handle as well as a properly set up swingaxle (not many do) and the trend was going way more Subaru than anything else, so it made sense to do them with the stock chassis and VW transaxle beefed up a ton.

Handling: in a straight line it was very civil and felt great.  Mildly aggressive driving it also did great, but when you really pushed it it just wasn't as good and had a violent "snap" point where there was no coming back from it... hold on and try not to get dizzy.  :-)

Carey what's your analysis of why the deDion behaves so unforgivingly in the Spyder?

I have a theory, which is that the swing axle's camber changes, particularly when combined with old school tire with round shoulders, cause the car to lose grip more gradually, and at a rate the driver can feel, which makes it more controllable (albeit probably slower) at the edge of its limits. The dD, in holding the wheels more perpendicular, probably handles "better" but eliminates the telegraphing feature of the swinger. Possible?

The DeDion held the road better, until it didn't, and then let loose in a manor that was just about uncorrectable.  I'm sure it has a lot to do with the lack of camber change.  This seemed to happen when you drove it on the edge, which most don't anyway, so for most it is/was a non-issue.  It is easier to adjust and you can change spring rates, compression, rebound, etc... with sock and spring changes, so that was an advantage and it really drove nicely in most instances.

Something else I didn't like about the DeDion (and this was just my own observation with little engineering to back it up): the Watts link is what holds it from having lateral movement, however the Watts link sits in the car at an angle, let's call it 30 degrees, connected to the chassis at the top and the suspension at the bottom.  As that suspension moves up and down the Watts link is also doing the same, on the suspension side,  but it is changing angle as it swings through its arc.  If you can picture this Watts arc and compare it to the suspension moving straight up and down, the Watts arc will actually pull the suspension slightly left and right, effectively unsettling the rear end, so you have a live axle that has a little bit of built in oversteer...  On small bumps, small compressions and rebounds, and etc that change is small  but hard bumps, suspension unsettling or hard cornering it increases the lateral motion.  

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