Hello my Original Equipment Sizes on tires are 225/50-17 at the front and the Original Rear Tires are
235/50-17. I had my rear wheels replaced since I had a piece of metal pop one of them so I had to replace both tires. When I went to discount tire the only size they had for the rear in stock was one size up for the rears and I was in another city with my wife trying to get back home when this all happened, it was a bad day lol. Anyway long story short my current setup is with still the stock fronts on at 225/50-17 but my new rears are 245/45-17, is this setup ok, the Z definitely does feel different driving. Not sure if this ratio is correct. Thank you for the help.

 

^^ Your current setup is not satisfactory. Your rears are shorter than your fronts.
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EDIT: TCS (if your car has this) and ABS wont' work correctly when the rear tires are shorter than the fronts.

 

So what should I do with the fronts, they'll need to be change soon, since I just changed out the backs.

 

You should mount the correct size tires on the front and the rear. Your front tires should be about 1/2" to 1" shorter (diameter) than the rears.

 

Got it fixed this morning at Discount Tire. They have terrific customer service I was told to pay the difference on the tires and that came to $169 altogether and then on top of that they took even more off for the hassle and for being given the wrong size so my total came to $82.00. Currently running at OEM Specs. Thank You!

Front Size
225/50-17

Rear Size
235/50-17