I know the 195/70/R14 is optional but can I go bigger on a stock '93 coupe with rubbing?

 

you can go as big as you like, but just keep this in mind, the larger the tire diameter, the more off your speedometer will be, and the more the steering angles will change.

I think your max tire size will be 215/40/R18, However you could use the 205/60/R15 these are used on the Z24 and would not change any of the steering angles or causing rubbing.

For a more certian answer you need to decided if you are looking at a larger rim and wanting a standard tire or low profile tire combo. Then I would check with companies like Toyo Tires and Perilli.

http://www.performanceplustire.com/p...15_SLASH_40-18

hope this helps..