I have a 2016 lexus is300 sitting at stock height with:

245/35/19 in front and 275/35/19 in rear. There is a noticeable gapnin the front but the rear tire is only an inch away from the fender. I want to lower it on RSR Springs to lower the front a bit, but im afriad i will rub in the rear with the meaty tire. Wheels are 19x8.5 in front and 19x10 in rear. What do you guys think?

Did those tires come stock or from aftermarket wheels. I know the stock 18 inch wheels comes with 225/40R18 Front and 255/35R18 rear. So if you use 275/35R19 for the rear it might be too big. Here's my suggestion.

Option 1: RS-R Down / Super Down - 265/30R19 - Rear

Option 2: RS-R Half Down - 275/30R19

we need the wheel offsets, but right off the bat, 275/35/19 is too tall

Most likely

Here's the RC 200T tire setup with stock 19 inch wheels.

Dunlop SP Sport Maxx
235/40R19 - Front
265/35R19 - Rear

but he has a IS not a RC. the IS has smaller tires than the RC.