I have an 05 G35X sedan. Will this size rims fit?

19 x 8.5 front 20mm
19 x 9.5 rear 30mm

Any help will be appreciated.

 

Never. First of all, you don't want to go staggered on your X- your traction control and AWD systems won't be very happy.

Second, those offsets are way off. An ideal setup for THOSE dimensions would be +38F/+45R. However, you are not going to go staggered, so 19x8.5" +38 all around will be perfect.

 

WHS^^Excellent advice VR. Definitly better to run same size all around with the X.