3 replies to this topic

[mariner]

Sometimes you see a small, detail idea which makes you think " That's very neat" - or at least, I do.

 

I saw just such a detail on a 1950's car at a local classic car show. Its a very special Lotus 6 with all envelping aluminium bodywork and a De Dion back suspenson instead of the Lotus 6 standard solid axle.

 

De Dion has several advantages over a solid axle of course - less diff. weight, inboard brakes if you want them, the camber and toe in stay just where you put them etc. One thing to avoid is letting the De Dion tube become a giant, high rate roll bar by not twisting it , or by giving it a means to twist easily.

 

Parallel radius links will stop it twisting but, being parallel anti dive/squat is harder to build in so it might be that a single radius arm each side is better - but then the tube twists.

 

On this car the twisting is allowed simply by having the two De dion tube halves be  connected by a screw thread on the outside of the inner tube and the inside of the outer tube. Result -  almost friction free rotation. In addition you can vary the rear track a good bit just by rotating the tubes off the car.

 

Its probably been used lots  times but when I saw it I thought it nice solution and much easier to fabricate than full sliding tube joint.

[carlt]

Sometimes you see a small, detail idea which makes you think " That's very neat" - or at least, I do.

 

I saw just such a detail on a 1950's car at a local classic car show. Its a very special Lotus 6 with all envelping aluminium bodywork and a De Dion back suspenson instead of the Lotus 6 standard solid axle.

 

De Dion has several advantages over a solid axle of course - less diff. weight, inboard brakes if you want them, the camber and toe in stay just where you put them etc. One thing to avoid is letting the De Dion tube become a giant, high rate roll bar by not twisting it , or by giving it a means to twist easily.

 

Parallel radius links will stop it twisting but, being parallel anti dive/squat is harder to build in so it might be that a single radius arm each side is better - but then the tube twists.

 

On this car the twisting is allowed simply by having the two De dion tube halves be  connected by a screw thread on the outside of the inner tube and the inside of the outer tube. Result -  almost friction free rotation. In addition you can vary the rear track a good bit just by rotating the tubes off the car.

 

Its probably been used lots  times but when I saw it I thought it nice solution and much easier to fabricate than full sliding tube joint.

not sure i understand how you stop the ends turning with only one trailing link - is the link solid mounted on the axle ends ?

anti squat is quite easy to build in with unequal/non parallel links 

[mariner]

Sorry, single and double radius arms refer to each side so there is one radius arm each side or two for double.

 

You can use unequal length or non-parallel side links but as soon as you do that you start to twist the De Dion tube unles it has an abilty to rotate in the middle.

 

One way is to slope BOTH the parallel side links upwards but that may generate big toe-in changes.

 

 

 

A simple slidng joint in the middle ( a la Rover 2000 by Spen King) requires fixed length drive shafts to resist side loads whereas the screw solution doesn't collapse on side loads.

 

Packaging De Dion in a race car is easy but double side links get nasty in saloons as the upper link either ends up in the rear pasengers' hip or the links have to be very short.

[rory57]

There is a lovely old single seater with Rover P4 front suspension and F-head engine and a neat De Dion axle which has two fixed length drive shafts and no centre joint in the De Dion tube.

 

How?

 

One (or both?) of the wheels has "open" roller bearings that allow the hub to move laterally relative to the bearing housing in the De Dion tube.