Originally Posted by
Paul Wilkinson
As I understand it (and my understanding is not great!) a Watts linkage, if restricted to a certain range of movement, generates a straight line i.e. the movement is straight up and down which is why they are preferred to a panhard-rod. The only reason I can think of for using the design as they did was that they were intending a design where the wheelbase would not alter throughout suspension travel. The S4 was rumoured to have originally been designed with either an independent or de-dion rear. I wonder if we have the beginning (or remnant) of a much more sophisticated (and expensive) design that was simply aborted part way through?
Kia ora Paul,
Mr Watt was a brilliant steam engine man and his idea was originally applied accordingly. He would be annoyed with Mr Chapman and rightly so.
Correctly used in the automotive world, a single Watt’s link can absolutely restrict the sideways movement of a rear suspension system and does so more accurately than a Panhard rod, which involves a radius of movement. Even so, the link does present problems in fixing the most desirable roll centre. There is no way the S4 set up, could have been satisfactorily used for front rear location in a more sophisticated system. More particularly in a de-dion rear end, where again a rigid connecting tube is involved thus coupling the links.
Sadly Mr, Chapman has no excuses in spite of the ongoing hype which follows him and you better believe it. LOL. 
Whatever, go here, click on “The Lycoming Special” and you will see how a real engineer goes about these things. 
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P.S. Trying again for a hot result!
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Cheers, Trevor.
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