Tire problem, or not ??

[Solomon Ngan <sngan@netaccess.on.ca>]

Hi,
I have been having problems with my tires (I think) since I put them
back on after the winter season.
They give me the "shakes" around 110 to 120 kph.  Sometimes as low as
100 kph.  The "shakes" are sometimes better, other times worse.
I have tires balanced, re-balanced and rotated, improved but still
there.
My tires are Goodyear eagle acquatred, around 70,000 km on 3 tires; only
30,000 km on the 4th one.
They still "look" ok.  Adequate tread left on tires.  Seems round.  I
have other tires shops inspecting them, they all can't find anything
wrong with them.
Could it be just tires getting old ?  70,000 is getting up there for
eagle acquatred, I think, although tread may still seem good.
But could it be something wrong with my '90 90q20v ? (I did not have the
shakes with my winter tires a few months ago.)

Any suggestions ?  Ways to isolate the problem ?  Any experience ?

Thanks,

Solomon Ngan