Compared to a 130/70-18 bias, I think the radial Avon 120/70R18 is not as thick and massive and therefore absorbs less energy, i.e. damps wobble less. The bigger thicker tires are a pig to steer, but they do absorb wobble better.
I ran a 130/70-18 Bias AVON VENOM on the front of my Concours and when it started to wobble I "snugged" up the stem bearings and it went away. The stem bearing were not overly tightened at all as once nudged past center the bars wound still free fall from side to side with the front wheel off the ground.
Then I installed a ZRX front end complete with a 17" x 3.5" rim and a 120/70-17 Radial SHINKO 005 ADVANCE with this install there was not so much as a hint of wobble at any speed under any condition. But now that there is some miles on this set up the wobble has returned that same as before; to which I've not tried to snug up the stem bearings as of yet.
Oddly the wobble I've had only appears when I'm slowing down through the 50 to 40 MPH range never going up through 40 to 50 MPH and will only be noticed if I have one hand lightly resting on the bar or less (no hands) if I've got a firm one handed grip or have both hands on the bars it is never to be seen.
I believe that any tire can wobble if given the opportunity and something induces it.