I haven't visited this thread for a while. Scooter62, I agree that the concept of a tubular space frame swing-arm is a good one. What I had a hard time with was Phil Vincent's absolutely ridiculous justification for it.
Like most of the design activity in that time, it was based on hearsay, good ideas, brainstorming sessions over a lot of beers, whatever!
In an article in one of the weeklies, Phil presented an analysis that showed that the twisting moment on the rear suspension, tending to twist the swing arm off its moutnings, was the equivalent of a doulbe-decker bus hanging off a 10' beam through the rear wheel spidle.
When I looked into his analysis, at the suggestion of my boss at N-V, I found he had assumed an infinite mass of the bike (i.e., no reaction to the forces being imposed) and infinitelly stiff tire (a rubber thing full of air?) and an infinitely stiff wheel (a steel rim with spokes).
If one took an opposite position, namely that the tire and wire wheel absorbed the entire shock, there was no justification for Vincent's design, particularly in view of the fact that when you hit a major bump, it was the FRONT wheel that took the initial hit. The rear suspension was along for the ride. Obviously, the real answer lies somewhere between these extremes. It seems incredible now, but all the high-powered computational dynamic analysis availble today wasn't there.
One of the projects I was trying to get started at N-V was a study of those basics. I had proposed a test at the Road Research Laboratory, which had an instrumented piece of pavement with a transparent plastic track section you could film things though. I proposed to run a bike at varying speeds across a 3" hgh curb, film the action with a high-speed cine camera and measure the forces between both the front and rear wheels and tires and the test strip of road. Motion of the bike in the vertical plane could be seen from the films.
RRL were very interested, because they hadn't done much research with motorcycles, but the proposal languished because of funding problems at N-V, until after my departure for a job at Boeing. Nobody else at N-V wanted to pursue it.
Looking back, I think we might have had some problems with the tires of the day, hitting a 3" curb at 90 mph or more!
I was originally hired by N-V becasue of my background in testing and the use of instrumentation, but it quickly became painfully evident that funding for such activitiy was very low on the priority list. That was my main reason for bailing out after a relatively short time.
