De Dion vs fully indepentent suspension
Discussion
Properly designed, independent rear suspension has marginal overall advantages compared to De Dion, but a well-designed De Dion installation is good enough to make it a very difficult choice.
De Dion can offer fixed camber in roll and squat, no jacking effect when cornering and – with the right linkages - an absolutely fixed geometric roll centre, none of which are easy to achieve with an independent suspension system without creating serious side effects elsewhere. In the kit car world, De Dion can also minimise problems due to incorrect geometry (whether due to poor manufacturing accuracy or poor assembly/set-up by the builder); an independent system with the wrong rear toe settings, for example, will handle like a shopping trolley with a wobbly castor, whereas it is easy to jig-up a De Dion so that the toe settings are automatically within reasonable tolerances.
Other pros and cons are very much down to the individual design; for example De Dions (and live axles) will usually incur some degree of roll steer due to the control arms. If you get a numpty design (like the Locost, with short, parallel trailing arms and a badly located Panhard rod), these can cause problems. If you get a clever design (like the Mallock TAM linkages or the asymmetric longitudinal Watts linkages used by Sylva), it can actually be turned to your favour to tune the handling characteristics beneficially.
On the down side for De Dions, both overall and unsprung weight are likely to be higher, camber of both wheels is upset by single wheel bump and, depending on the spring base, the force of a bump at one wheel can be partially transferred to the other wheel.
To be honest, the reason it is retained by all but the most recent Caterhams is mainly historic (the Lotus Seven was based on the Lotus Eleven chassis, which was originally designed with both live axle and De Dion variants) and Dax probably adopted it to ape Caterham, but it has enough benefits to remain a valid design choice.
De Dion can offer fixed camber in roll and squat, no jacking effect when cornering and – with the right linkages - an absolutely fixed geometric roll centre, none of which are easy to achieve with an independent suspension system without creating serious side effects elsewhere. In the kit car world, De Dion can also minimise problems due to incorrect geometry (whether due to poor manufacturing accuracy or poor assembly/set-up by the builder); an independent system with the wrong rear toe settings, for example, will handle like a shopping trolley with a wobbly castor, whereas it is easy to jig-up a De Dion so that the toe settings are automatically within reasonable tolerances.
Other pros and cons are very much down to the individual design; for example De Dions (and live axles) will usually incur some degree of roll steer due to the control arms. If you get a numpty design (like the Locost, with short, parallel trailing arms and a badly located Panhard rod), these can cause problems. If you get a clever design (like the Mallock TAM linkages or the asymmetric longitudinal Watts linkages used by Sylva), it can actually be turned to your favour to tune the handling characteristics beneficially.
On the down side for De Dions, both overall and unsprung weight are likely to be higher, camber of both wheels is upset by single wheel bump and, depending on the spring base, the force of a bump at one wheel can be partially transferred to the other wheel.
To be honest, the reason it is retained by all but the most recent Caterhams is mainly historic (the Lotus Seven was based on the Lotus Eleven chassis, which was originally designed with both live axle and De Dion variants) and Dax probably adopted it to ape Caterham, but it has enough benefits to remain a valid design choice.
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