Matt Spencer wrote:
The stiffness bit , theyre on abouZero Lateral complance , when leant over , locks the suspension . Gets a bit bumpy .
Theory being , if leant over at say 45 deg , a degree (
) of sideways flex is necessary twixt frame & wheels ,
assumeing a flatish track with bumps & irregularities . Rather than banked speedway type ' turns ' .
Moto G.P. etc .
Sideways flex between the frame and wheel can be achieved at the swinging arm...neither Rickman nor Seeley arms were heavily braced like later designs, but the Rickman is typically much smaller diameter tubes and no bracing at all. I suspect the change to rubber bushes on the Rickman however was originally designed to give this flex, because none existed in the frame, in effect it 'amplified' the feedback from the contact patch to let you know you were near limits. I am pretty sure all Seeley frame designs have some flex built in, and they typically use a larger diameter (stiffer) swinging arm, letting the frame itself do the job of flexing in the turns. How far this carries forward to a modern Seeley replica versus an original is mute, since the tubing chosen often provides a stiffer frame! But again, this works with modern tyres (radials), which have different characteristics anyway.
The issue I came up against was the drive train compressing the rubber bushes longditudinally...forcing the wheels out of line under acceleration, specifically producing unwanted effects transitioning from braking to power mid corner. Phosphor bronze, or taper/needle rollers etc. limits that occurance.
A number of Rickmans have been fitted with stiffer braced box section swinging arms, maybe too stiff! Mine will retain a round tube item, but with a small cross tube brace, hopefully enough, and not too much, probably it won't make that much different because the arm is a little longer too, which would produce more flex....the length was to allow a wider tyre to clear the round tube, and to allow the swinging arm to still clear the frame....that radial tyre will also grip far more than a '70s tyre, but probably have its own sidewall flex.....
All of this really suggests that whilst interesting to consider how well things worked in the 60s/70s, you are playing with a rather different toy once you change rim sizes (dia and width), tyre widths, tyre constructions, tyre compounds, frame stiffness, swinging arm stiffness, typically stiffer springing and improved damping, and altered geometry at least from typically longer dampers etc. if not from altered head angle as well!