Summer tires mess up handling

[the Spaeth's]

Our 91 TQ Avant does the same thing. I believe the same size tire. The tires
tramline to a scary degree. I have had very careful alignments done. I have
one of the Bernie style upper bars to get it all they way dialed in. We are
running H&R springs with Koni adjustable struts. There is no indication of
this with the 16" snows. It drives fine with the snow tires on it. I have
thought about dropping back to 16's for the summer. Could this be caused
more by the actual tire design than just the size of tire? I don't want to
spend that much on new tires just to have them do the same thing again. I
have tried different air pressures but it didn't seem to make much
difference.

Craig