I have 215/55/17 up front and rear.

My car is RWD; I used the tire size calc and was thinking of running 245/50/17 in the rear only and keep the 215/55/17 in the front.

1.8% off

Would that be fine to run different size sidewalls? and would 245 be too large in the rear? Any rubbing do you think?? Not lowered at all and driving a boosted sedan. Planning on ordering tonight