[socratic]

2001 Boxster here. The previous owner put on some new Kumhos before selling and I presumed they were balanced. But the car started vibrating at about 80mph.

I took it to a shop with a Hunter 9700 wheel balancer that does a "road-force balance"; that is, it applies a 1000 lb force to simulate the car on the road.

Let me describe the results this way: If the original state was 0% and a glass-smooth balance was 100%, then the job they did was like 80%. I still feel a bit of a vibration. I am now hearing through this thread and other places that Porsches are finicky. I will bring it back to them and ask them to check it again since it's only been a few days since I did the balance.

The place I went to also had a new machine (their Hunter 9700 was old they said). It is a machine called a "John Bean" and it looks "higher tech" using lasers to measure out of round wheels. But it did not have "road-force" and so I asked them to use the 9700. Maybe I'll ask them to use the John Bean as a '2nd opinion".