Tire vibration can by rather dynamic -- good shocks will absorb quite a bit of it, and the road surface can change it as well -- if there is a repetative roughness to the road, it can either dampen or enhance the tire vibration.

It will also react to speed -- as some rotational speeds you might have one tire "bouncing", at others two, etc. Springs have an effect here as well, ditto for tire pressure.

Check the front end alignment if you have more wear on the outside of the tires than inside -- this is usually an indication of excess toe (out, I think) -- this may be due to worn tie rod ends or drag link ends.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!