I have an 04 XJR with approximately 40k miles on it. I love the car but have always been a bit annoyed with a speed specific vibration @ 60-65 mph. I understand that the XJ8 is pretty particular regarding wheel balance/ radial force variance. I had GoodYear Eagle F1s for a while which were pretty bad. I changed to Yokohama Advans which areaceptable but still exhibit some vibration. I still think however that an 80k car should ride without any vibration. I have balanced this set of tires twice in 15k miles. RFV ranges from 6 lbs to 16 lbs.

Questions

Is minor vibration on a 19" low profile tire normal and to be expected?
What is a reasonable RFV to shoot for when balancing/match mounting?
If acheivable, should a 6 lb RFV on all tires have any vibration?
What are other possible problems causing this?

Any thoughts appreciated.

KMSCHAER