Chassis Design & Construction

The frame of the FWS1000 was typical of the TT-F1 era. It is a wide perimeter twin loop ‘diamond’ style made from steel tube. Constructing a replica from the available photos seems a straightforward enough process until you begin to delve into the intricacies of motorcycle chassis design.

There are many aspects to consider in the design including basic dimensions like rake, trail, weight bias and wheelbase. Fortunately, the Japanese RACERS magazine vol. 10 featured the Honda V4 line of racing bikes and included a specification table with a number of handy dimensions.

The FWS1000 raced with a 16” front and 18” rear wheel combination. Our replica will use 17” wheels front and rear so we have to consider how that will affect the geometry of the chassis and suspension as well some practical issues like front tyre to engine clearance etc. One critical piece of information is knowing where the centre of gravity is located. When you don’t have a physical object to measure the best you can do is estimate where it is. It’s important to know because it has a direct bearing on rear suspension squat behaviour and where to locate the swingarm pivot in relation to the engine’s output shaft.

So along with some help from Tony Foale and John Bradley and a healthy dose of the ol’ suck it and see approach, it was time to start drawing.

Now that we’ve established the basic chassis parameters it was time to start building. We began with making and setting up the steering head tube, swingarm pivot and suspension link parts.

With those components in place we could start with fitting up the tubes. Let the bending, cutting, grinding and welding begin!

A special shout out to Darrin Treloar for helping us with his tube bending prowess. It’s always good to have a world champion in your corner.

With the main frame completed it was time to turn our attention to the subframe. The tubes of the subframe wrap tightly around the rear cylinder head particularly on the left hand side and form the upper mount for the rear shock and seat unit. Bending the tubes and arranging the fixturing was quite a tricky set up.

With the fixturing in place the subframe structure was welded in place.

The frame is released from the fixture and we can start to see a motorcycle emerging!