I'm still on the OEM Metzlers at 20K, and the wobble seems to come and go. I'd also want to believe the front tire is part of the issue, and perhaps the fork rake angle sets off a harmonic vibration? Kind of like sticking a big old tuning fork out in front? Don't know for sure.
To further regale [read-bore] you with yet another truck driving story from my days of yore: I used to haul Fruehauf J model dry bulk trailers (aka cement tankers.) When loaded at around 45 MPH, the entire 80,000 lb vehicle would find a harmonic and jump up and down around 1/2 inch, at say, 2 or 3 cycles per second. With the inertia of 40 tons hopping up & down, it felt more like it was jumping up & down a half a foot or so. Some flat beds will do this too, if you load them just so. What does that have to do with anything? I'm not sure, but since I've finished my first double coffee of the day, the keyboard is at my mercy.
See also - traffic jams on a suspension bridge, where the entire 4,000 foot long road deck mass is hopping up and down an inch or three. I hate it when that happens...
