I bought my 89 RS with American Racing wheels that are 15x8 and the offset is wrong they rub horribly they ride terribly and are robbing the car of handling power. That said, I'm thinking about going original with a nice set of OEM red 15's but I am wondering how big of a handling improvement would a modern 17' version be and how much of a problem with rubbing (so sick of rubbing!) would that give me? Thanks in advance for input guys. Oh, and if anyone has any red 15' OEM wheels I might be interested.

 

Most 3rd gens with 15" wheels and 215-65-15 (or similarly sized tires) handle in the 0.80g range on the skidpad. Moving up to a 245-50-16 adds 0.05 to 0.10g, and going up to a 275-40-17 will put most 3rd gens well into the 0.90g range or higher.

The combination of more tire width, less sidewall, and better performance tires gives a huge performance increase in grip in all 4 directions.

Others will surely chime in.