Can I run my old 2003 G35 Coupe winter tires (Front:225/50 R17, Rear 225/55 R17)on a 2013 Sedan? Will it impact the Speedometer, mileage calculation, ....

 

The rears are pretty tall vs. the fronts (about 3.3% higher), should work, but best to stay under 3% difference front to back from all I've read. If you're wanting to use these as a winter set I think I'd just get a pair of 225/55s and match the rears up (assuming all the tires have the same wear). And if your Sedan is an S model they won't clear the big brakes, but otherwise should be ok.