Tires: tires, tire placard, doorpost

Question
I purchased new tires for my Saab 5 months ago. I recently learned they are the wrong size.  How does this affect the car?  Can I return to the seller and demand replacements?
Debra

Answer
Debra,

Let's start at the basics:

On every vehicle sold in the US, there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size.  The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.

OK, so are the tires the same size as the placard?  If yes, then you do not have a problem.

If no, then there MIGHT be a problem.  But to be sure I need to know what the placard says and what the new tire size is.

But it is possible there might not be a problem at all.  So let's get the details and go from there.  

Looking forward to your repost!