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. 

Jim Olson

 
"The Toys"...!!!  Save the Wave! 

 Where I've been in a Corvette...!!!

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.