Need help with vibrations

[JoeFromPA]

Hey all,

I know cars well but I don't yet know the boxster's weak points well, or what are known to cause rotation-related vibrations.

I'm running a set of 18x8/18x10 Porsche wheels with near-new Michelin Pilot Sports (NOT PS2s). I can confirm that when they first went on, their balance was superb.

After driving the car about 1000 miles, I've got vibration issues at a variety of speeds and situations. At around 45mph the wheel shakes, then evens out with some minor vibrations above and below it. 80+ starts to get really bad. Around 70 it gets twitchy weird. 75 is baby smooth. 65 is smooth.

There is no notable bends in the wheels. I have a set of winter tires I'm going to rotate on to see if it smooths it out, which would show me that it's balance or tire related.

If not, are there any known issues with the boxster suspension/control arms/links/bushings that could cause something like this?

If it is the tires, I'm going to get them road force balanced at a local shop.