There's so many things that can contribute to high speed wobble, aside from the head bearing adjustment and having good tires, the "fix", if one is ever found, seems to be extremely inconsistent.
People have found a cure to wobbles in....
head bearing adjustment
new front/rear/both tires, or switching brands/tread types
Lowering the front
Progressive fork springs
progressive rear shocks
adding a steering damper
adding frame braces/solid motor mounts
adding a fork brace
re-torquing the swingarm pivot
switching to radial wheels
playing with front fork pressure
playing with rear shock preload
playing with tire pressure
removing the passenger sissy bar
.....it goes on and on. What works for one person may not work for another.
From research I've done the most root cause of speed wobble is slight vibrations/oscillations that start within the sidewalls of the tire. This happens regardless since no tire is 100% absolutely perfect, but shorter/stiffer sidewalls(like radials) are much more resistant. Heavier bikes, by virtue of having more inertia from more mass, and more resistant. The bike's suspension has a lot to do with absorbing/controlling this as well.
It should also be noted the Vmax(and many other 80's bikes) are known to have mis-aligned frames right from the factory, in which case a wobble may be essentially in-curable if the frame is not straightened first(such as with Compu-Trak). People who have have the frame aligned report significant gains in handling and stability.
Mine used to have a really bad speed wobble in that 110+ range. Switching to ME880 tires seemed to help somewhat, it wasn't as pronounced/violent as before. PCW internally lowered the forks and replaced the head bearings with OEM parts. On the drive home I ran it to 140 and it was solid as a rock. At their advice, I removed the soft, cheapo ebay shocks and replaced them with the stockers. Next time I ran it up again, a bit of wobble creeped in around 130. Not horrible, but noticeable.
Since then the problem is "mostly" solved. If I lean forward, and put my feet on the highway pegs, I can run the bike as fast as I like and have no to minimal wobbles. It very rarely is bad enough that I need to back off. That said, I need to run up in fifth, since the 4-5 shift at 130 greatly upsets the bike and causes instant wobbles that don't settle out. Currently the rear shock preload is maxed out, which I have heard can sometimes make the problem worse(and I had NO wobbles when I briefly drove it with the spongy ebay shocks), so next time I'm out I will try turning the preload down to see if that helps.
