Summer tires mess up handling?

[Thomas Mesich]

All winter my 200 20V has driven perfectly with stock wheels and 215 60
15 Blizzaks.  Now I have put the summer wheels and tires on I have a
problem.  They are Momo wheels with 235 45 17 Goodyears.  On the
Blizzaks the car drove straight and true and very solid.  On the summer
tires it tends to pull to the right and feels generally loose.  The car
was aligned last fall.  Any ideas?  Could the front end be flexing due
to the larger, heavier tires?  I am confused.

 

Tom in Elk River, MN