Many years ago, my car then (not P5) with front tires 235/45-17 would exhibit the front end shimmy whenever I got on the freeway and accelerated up to speed 65-70. The on-ramp is located a couple of miles from home. I also had the front end suspension checked and force balanced the tires on the Hunter machine with no improvement.
One day while I was cleaning the engine in my driveway, my German neighbor came by and shared a couple of non-chilled brews; more potent that way I guess. We somehow got on the subject of the front shakes on my drive to work everyday. He looked at my tires and provided a possible explanation why that would happen. He says, you have low profile tires and they are probably a little under-inflated (they were). Overnight the tires take a "set" because of the weight of the car. All 4 tires take a set, but the front end is more prone to shimmy because that end is looser. He says, try this...Instead of getting on the on-ramp right away, drive around for a few minutes and get those tires warmed up, then get on the freeway. I took his suggestion and damn was he right. No shimmy or shake. May not be your problem but wanted to share anyways.
