Would 18x11s fit the rear of 11-13's?

I have brembos up front, so ill need 19x9 up front and I wanted 18's for better tire selection/pricing in the rear. Is it a bad idea to have 19 up front and 18 in the rear?

 

This is sortof an odd tire combo.... Generally, if you go smaller rear wheel to give you more tire (generally we're talking drag tires at this point), we're talking like 16" that allow some serious meats.

Brembo cars can fit 18's up front, just not all 18's -- the more limiting factor is the clearance between the inside of the spokes and the sides of the caliper. American Muscle sells plenty of 18's that fit on the front of Brembo cars.