Normally the tire size is as follows. As 17" the 45 series usually goes on the front with a smaller tire in width. The reverse for the rears. For example:
225X45X17 in the front
245X40X17 in the rears
The wider tire stablelizes the rear end but maintains the overall circumfrence of both front and rear. Having the same size tires with different ratios is a little questionable. This may sound silly or there is not intension to be rude. Can you double check the sizaes again. How did you end up with these tires and placement on your car?
Andre