De Dion rear end design..

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Brian P
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Re: De Dion rear end design..

Post by Brian P » Thu Aug 31, 2017 9:30 pm

Don't forget the one BIG bad disadvantage of using de Dion suspension: the advertising folks can't shout out "LOOK! 4 wheel independent suspension!"

englertracing
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Re: De Dion rear end design..

Post by englertracing » Fri Sep 01, 2017 12:13 am

The testing was done in the 60s I believe.
Also regarding the full independent....
Usually the trophy trucks and truggys finish the Baja 1k before the irs buggys :D

lemons racer
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Re: De Dion rear end design..

Post by lemons racer » Sun Jan 21, 2018 3:27 pm

The De Dion was used allot back in the 50s-60s mostly by european manufactures that could not afford to produce a full independent suspension which is MUCH more expensive to develop. The advantage of the De Dion is less unsprung weight compared to a live axle and that's about it.
The last car I worked on using this suspension was a Montaverdi Hi (forgive my spelling, this was back in the mid 80s)) built in 68, 1st of 2 built. 426 Hemi, ZF transaxle, the car looks something like a Bora. When under that car it was less than impressive although I was told when new it was clocked at 189 mph.

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Re: De Dion rear end design..

Post by pdq67 » Mon Jan 22, 2018 6:46 am

^^^^^^^^^^^^^^^^^^

"When under that car it was less than impressive although I was told when new it was clocked at 189 mph."

I wonder how fast my next door neighbor's 440/4-speed equipped Jensen interceptor is?

pdq67

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Re: De Dion rear end design..

Post by Ratu » Mon Jan 22, 2018 1:24 pm

Beware the assertion that IRS is truly independent for it is not. A bump at one wheel affects the opposite wheel. To avoid that completely the spring rate would need to be extraordinarily soft indeed, certainly very soft in roll, i.e. one wheel bump (theoretically offering no roll resistance at all!). Either that or the car itself would have to be extraordinarily heavy. A force delivered from one wheel and affecting the sprung mass necessarily means that there is an effect on the opposite side suspension. If there is an anti-roll bar then the loss of independence is increased even further. Beware the potentially misleading term "independent".

De Dion is interesting in that it allows lower unsprung mass than does a live axle. Apart from that it can be made to exploit most of the advantages of the beam axle. There is also one extra possibility. During cornering one may arrange for the wheels to camber inward (towards the apex). That is not something I have ever seen actually accomplished with IRS (although theoretically possible with a very elaborate system of links). Years ago the late Spen King delivered an interesting lecture about suspension where he mentioned this possibility. It could be achieved by splitting the de Dion tube into two portions wherein there was a rotational joint between the portions allowing for freedom for rotation of the tube portions along their major axis. Clearly the geometry of the locating arms would need to be correct, but with pencil, paper, compass, set-square and a little time it does not take much time to figure it out. You can even make a model with cardboard, using drawing pins for the pivots. Of course CAD is the most convenient way to experiment with this, still the old fashioned ways have a charm of their own and they reward the experimenter with a tactile, physical insight.

Later I discovered that the same effect as this can be obtained with a torsion beam axle so long as the axis of the torsion beam passes behind the centreline of the wheels. This very scheme was developed for the rear suspension of the Australian Ford Falcon as an alternative to IRS. It was a whole lot lighter and much cheaper to manufacture, but despite excellent potential, reliability and functionality it was dropped and the IRS was adopted instead due to a strong intervention from the marketing department...

On a related note, I recall the Donovan V-8 powered Alfa Romeo Alfetta raced by the Algie brothers in New Zealand, of all places. It featured a de Dion rear suspension just like the standard car. It was very competitive and in the wet it was unbeatable. The drivers mentioned the car was very forgiving in its handling and provided an excellent tactile feedback to the driver. Interestingly in the modern mid-engine era Ferrari built a F-1 car which could be readily swapped from double wishbone to de Dion and back again. Drivers who tested it ran identical lap times with double wishbone and de Dion. They stated that the de Dion felt better, giving more feedback and being more forgiving. In the end Ferrari stayed with double wishbone due to attributes of easier adjustability in the pits on race day, as well as for aerodynamic reasons.

Meanwhile over in Australia there have been people experimenting with beam axle front suspension for a road race car. I first heard about it early last year and have been asking around about it since. So far it is confirmed it was used on a Super Sedan with some success. I find this intriguing and have been keen to know more about what it is like and the reasoning behind its use.

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Re: De Dion rear end design..

Post by Leftcoaster » Mon Jan 22, 2018 9:30 pm

Ratu wrote:
Mon Jan 22, 2018 1:24 pm
De Dion is interesting in that it allows lower unsprung mass than does a live axle. Apart from that it can be made to exploit most of the advantages of the beam axle. There is also one extra possibility. During cornering one may arrange for the wheels to camber inward (towards the apex). That is not something I have ever seen actually accomplished with IRS (although theoretically possible with a very elaborate system of links). Years ago the late Spen King delivered an interesting lecture about suspension where he mentioned this possibility. It could be achieved by splitting the de Dion tube into two portions wherein there was a rotational joint between the portions allowing for freedom for rotation of the tube portions along their major axis. Clearly the geometry of the locating arms would need to be correct, but with pencil, paper, compass, set-square and a little time it does not take much time to figure it out. You can even make a model with cardboard, using drawing pins for the pivots. Of course CAD is the most convenient way to experiment with this, still the old fashioned ways have a charm of their own and they reward the experimenter with a tactile, physical insight.
The 1963 - 1977 Rover P6 employed a rear differential with integral disc brakes mounted to the chassis, and a De Dion suspension with trailing arms, a transverse beam with halves that slid and rotated within a sleeve as you describe, and fixed length half shafts which maintained track within their arc of travel

The geometry was successfully tweaked by club racers but the differential unit proved incapable of supporting the torque and horsepower outputs of developed alloy BOP V8 engines, and was most commonly replaced by Jaguar IRS units

To create a wide engine bay without intruding Mac Pherson strut style towers, an ingenious disc braked front suspension placed its shocks vertically and the springs horizontally; all exterior panels were bolted to the steel frame, and with alloy fenders, hood, trunk, and roof, the UK 3500S with V8 and auto trans weighed around 2850lbs

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Re: De Dion rear end design..

Post by Brian P » Tue Jan 23, 2018 7:17 pm

I suspect that modern tires are insensitive enough to camber that the bad side effects of having camber change fully compensated or over-compensated for body roll outweigh the good.

While it is theoretically possible for a twist-beam-axle rear suspension design to cause the tires to lean in when the car body leans out by having the twist-beam aft of the wheel center-line, in practice this is never done. Some twist-beam axles have the twist beam in line with the wheels (chrysler K-car, gm X-car, early VW Jetta Mk6 before they switched back to IRS, and some older Toyota and Suzuki small cars were like this) which gives "beam axle" geometry - the wheels stay straight up and down regardless of body roll - but the far more common design has the twist beam aft of the chassis-end pivots but in front of the axle centerline, which only partially compensates for the camber (depending on how forward the twist-beam is of the axles). Cars with twist-beams like this include VW Golf Mk1-2-3-4-7, Honda Fit, GM everything newer than the X-cars and A-cars, Ford Fiesta, Fiat everything that uses a twist-beam, Renault everything that uses a twist-beam, Citroen everything that uses a twist-beam, etc.

Large camber changes (on both sides!) just because you go over a one-wheel bump are just another way of upsetting the chassis.

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