That is a little more interesting. It is not specifically in the rules of Class C, but in the overall rules of general vintage bike provisions where it says "Monoshocks are prohibited, except for Vincent Grey Flash." Although I was the first to run a coil over on the back, I always felt that their use of the term monoshock would prevent them from giving me a hard time. Nobody blinked!
From that point, all you can argue is semantics. I think the broad definition of a shock absorber is a device that is fitted to a wheel to reduce the effects of traveling over rough ground. With the advent of friction dampers, it usually meant a spring and a damper combination. With the further introduction of hydraulic dampers it usually meant the same, however, in 1951 Monroe developed the Monroe-matic, which was a telescoping damper inside a spring. From this point on the more modern popular conception is that the shock absorber is the damper.
I think it is difficult to argue that the Vincent rear suspension is a dual shock suspension because it uses two springs and a single damper. You would also have to concede that the Girdraulic is a dual shock suspension, because it also uses two spring with one damper. If you looked at the modern Works Series D coil over you would have to argue it is three shock absorbers because it has three separate springs. Things start to get weird.
It is possible that here in the States the Vincent has always been considered a monoshock, despite its use of two springs. It was clearly not the same as the Harleys and Indians.
David
