What would be the tallest (profile) practical 195x15" tire to fit without clearance problems onto a 93 del sol with standard height suspension.
Reason = higher gearing for better highway gas milage.

 

The OEM tire size off the dealer floor for a Del Sol is 185/60/14 which carries an overall diameter of 22.8" Now, Most people can run 195/55/15's which is an Overall Diameter of 23.5" with little to no issue even lowered 2-3" or so because it depends on the offset of the wheel. My personal opinion is that the largest 15" Tire you could run would be 195/60/15's which are an overall Diameter of 24.2" and are pretty much the largest size you could run without rubbing issues. If you bumped it up one more profile to 195/65/15 you would be looking at a a 25.1" Diameter tire which on a Civic/Del Sol would have some rubbing issues on bumps/corners.

-Froth