rj
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| posted on 12/6/15 at 11:46 AM |
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Caterham De Deon tube dimensions
hi
I am having a bit of a re think regarding my rear suspension, it is currently a MK De Deon tube, located by 4 radius arms plus Panhard rod. I have
been doing a lot of reading via the search funtion plus google, I think my radius rods are too short - they mount just in front of the driveshaft,
Caterham ones mount approx 4-6 inches further back, and the Panhard rod puts my rear roll centre near the centre of the de deon - hight wise, the
Caterham lower A frame picks up on a lower extension to the de deon, and I understand the roll centre is at that point i.e. the A frame/ de deon
connection.
So, I am thinking of basicaly coping the Caterham set up, has anyone got drawings/dimemsions for the A frame/ De Deon/ radius arms- or the
longditudinal Watts linkage found on some.
If you think my idear is just crap, please feel free to say !
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MikeRJ
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| posted on 12/6/15 at 12:27 PM |
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Note that using an A frame + two trailing arms puts torque through the De-dion under braking which isn't present when you have four trailing
arms. Obviously the axle needs to be strong enough to cope with this, and axle failures on Caterhams are not unknown.
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Sam_68
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| posted on 12/6/15 at 02:16 PM |
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quote:
Originally posted by rj...or the longditudinal Watts linkage found on some.
The Caterham longitudinal Watts linkage is a bodge of the worst kind, when considered in terms of the Lotus/Chapman 'ethos'.
It was a cobbled-on fix to the problem that Mike identifies. Chapman must be spinning in his grave/South American Tax Haven...
A properly designed and engineered 5-link is arguably superior, though there are more sophisticated methods of lateral location (Watts, Mumford or
WOBlink) if you feel the need.
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craig1410
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| posted on 13/6/15 at 12:29 AM |
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I'd stick with the 5-link suspension. That's what I went with on mine having studied a good few books on suspension design.
Take a look here: http://www.meerkats.uk.com/meerkat-rv8-build/?tag=de-dion
Cheers,
Craig.
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Minicooper
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| posted on 13/6/15 at 07:40 AM |
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quote:
Originally posted by Sam_68
The Caterham longitudinal Watts linkage is a bodge of the worst kind, when considered in terms of the Lotus/Chapman 'ethos'.
I never heard of anything referring to Caterhams which would describe them this way, they are one of the best handling cars I have ever been in
David
[Edited on 13/6/15 by Minicooper]
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Sam_68
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| posted on 13/6/15 at 08:47 AM |
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quote:
Originally posted by Minicooper
I never heard of anything referring to Caterhams which would describe them this way...
You have now. 
Caterhams are well-developed, but that doesn't stop it being a flawed design - it just means that they've been dogged enough to
successfully mask the flaws to an acceptable degree.
But they've never had the confidence to go back to a clean sheet of paper and do the job properly.
This is by their own admission - they have openly stated that the reason they moved from a live axle to a de Dion was simply because they felt they
lacked the resources to develop a proper IRS (despite the fact that even one-man-bands like Jeremy Phillips have managed admirably).
The result is that when power outputs and grip outstripped the very limited torsional stiffness of the original Lotus Seven chassis, instead of
designing a fundamentally better chassis, they just added extra tubes where they could.
When braking loads started to cause problems with the suspension flexing, instead of re-designing the suspension properly to address it, they added on
a full upper wishbone at the front, in addition to the ARB that formed part of the wishbone on the Lotus Design. And at the back where - as MikeRJ has
pointed out - the A-frame + single trailing arms were allowing torsional deflection of the de Dion under increased braking and acceleration, instead
of re-designing it properly to give a system of location that was both geometrically correct and stiff enough to take the loads, they just
superimposed the complicated and geometrically flawed Watts linkage to brace what was there already.
Sure, it works well enough, but it's inelegant, and it could work better, be cheaper and lighter, if it had been done right. Sorry, but I
stick by my original words - in engineering design terms, it's a bodge.
The Lotus/Chapman ethos, by contrast, has always been to get the design right in the first place - to hell with development. If your
design doesn't cut the mustard any more, you replace it with a competent one that does.
Remembering that Chapman actually threatened to sack the first man who added a (necessary, as it turned out!) extra link in the rear suspension of the
Esprit, how do think he would have felt about adding an extra six links on top of what as already there on the Seven, just as additional
bracing serving no geometrical function (and in fact adding an additional geometrical conflict)?
[Edited on 13/6/15 by Sam_68]
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rj
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| posted on 13/6/15 at 06:00 PM |
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Thankyou for your comments, I can see how 4 links are better for coping with torque for braking / acceleration, although it didn't occur to me
prior to it being pointed out ! I have done some more googling and think I will go for a Mumford link, and move my radius rod mounts as far back on
the de deon as possible, and make longer links.
The reason for my plans are recent experience of a Caterham de deon - went and handled superb, probably helped by a 310 bhp 2.3 duratec ! and a MK
Indy RR. In comparison mine understeers and I struggle to get any heat into my front tyres. It got me thinking about various tweeks, I am in the
process of fitting a rear ARB ( might fit a front one also ). I think an issue is that my rear roll centre is a lot higher than the front, thus the
plans to lower it.
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