Wobble and Weave video

[Richard230]

If you can use a little entertainment today, check out this 1975 Dunlop video showing how stable motorcycles of the day were when exceeding the speed limit:   

https://www.youtube.com/watch?v=z3OQTU-kE2s

[Shinysideup]

So Richard, as an engineer, how do you explain how this issue, which the film attributes to the point of steering being forward of the contact patch due to rake, has been largely resolved in modern machines?

I've only had one machine go into a dangerous weave and that was due to a binding head bearing that was incorrectly torqued by a local shop.

[flar]

From the Wikipedia article, it looks like several design factors of tires and frames can improve the situation so modern tire technology and modern stiff frames probably help a lot:

Since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon."[2] The top five influences on wobble have been found to be lateral stiffness of the front tire, steering damper, height of bike center of mass, distance of bike center of mass from rear wheel, and cornering stiffness of the front tire.[3][6]

An academic paper that investigated wobble through physical experimentation and computer modeling concludes: "the influence on wobble mode of front tire characteristics, front frame inertia and chassis stiffness were shown. In particular, it shows that [by] increasing front tire inflation, chassis stiffness, and front frame inertia about steering axis and decreasing sideslip stiffness of front tire, wobble mode damping is improved, promoting vehicle stability."[7]

[Richard230]

I am pretty sure that stiffer frames, better suspension, better tires, improved weight distribution and 40 years of engineering knowledge has made motorcycles a lot more stable than they used to be.  No doubt "ambulance chasing" attorneys and manufacturer racing programs have helped push the technology along too. 

I might add that I am reading a book about BMW motorcycles and it mentions that the 1974 R90S was not very stable at high speeds, but reinforcing the frame and installing the RS fairing in 1977, which was designed in a wind tunnel, made a significant improvement in the high speed stability of BMW's largest model at the time.