You didn't specify width, but I believe grids in 18" only came in 9.5" +15.
With that said, 9.5 +15 will fit & they will clear the coilovers. However, the only way you can be low with that size is stretched tires with a slight roll, slight pull, and camber.
Matter of fact, here's a pic of Grids 18X9.5" +15 on a S14:
He's running 225/40 up front and 245/40 in the rear.
You could try running a monster stretch with 215/40 all around or a less extreme stretch with 225/40 all around if you want to get low.
