I would loosen up the front end and do an alignment first off and see if that makes a difference. Takes much less time than changing a tire and you can then eliminate that as a cause. I would think its possible that an alignment that is out a bit could be effected more with some tires than others. I had a slight wobble with a PR4 that went away after some winter maintenance that included an alignment. Unfortunately, I did a few other, possibly related things, so I cant say for sure that was the solution. I have since changed out the PR4's and have to say that I am less a fan of them then I was before. Now that I am running another brand, I can say that although they stuck well, they seem a little on the soft side and dont give feedback to the rider as well. The term wishy-washy comes to mind (sorry, cant think of another way to describe them)