My question is: will 11 inch rear wheels (ZR-1) fit my 95 base Convertible? I would love to put the 315/35ZR17 Michelins on my car but not sure they’ll fit. Was the ZR-1 set up wider to handle the wider rims and tires? 

thanks, Mark

Short answer - yes, the rear bodywork on the ZR-1 was 3 inches wider than the regular C4.

There were two different sizes of wheels for the GS.  The convertible's wheels, front and rear, were a bit narrower than the coupe's.  That's why the coupe had the little added on wheelwell flares and the convertible did not.  This article points out a few things that were special about the Grand Sport.  #7 is on the wheels and tires.

A good friend has a regular '94 coupe and has the wider wheels on it.  He has chosen not to add the wheelwell flares and they definitely fill out the wheel wells. 

I'm a little late seeing your question but here's my answer anyway.  I bought a set of Grand Sport knockoff's from OE wheels, 17x9.5 front and 17x11 rear.  I have Nitto NT05, 275/40-17 front and 315/35-17 rear.  They fit my 96 Collector's Edition coupe perfectly.  No rubbing front or rear.