Tires: tire rim width, stock tire size, rim width

Question
My stock 18" rim width is 7". The stock tire size is 225-45/18's.

I was contemplating putting some Michelin 235-45-18's to give me
a quieter tire with a little more rubber on the ground. I read
where the 235's recommend a minimum rim size of 7.5".  So, should
I not put this tire on my 7" rims, what negative effects would I
run in to if I did?   Thanks.

Answer
Gib,

If you put a tire on too narrow of a rim, the tire will tend to arch across the tread face.  That not only will probably result in excessive wear in the center of the tread, but also make the car directionally unstable.  It will feel like the car follows the ruts and grooves in the pavement, as well as being sensitive to wind.