Depends on the width of the rims you're running. You can squeeze in a 185 but I recommend getting new rims. Price can range from 30-50k for decent rims.
To stay on the safe side, you can go for 6.5-7.5 inch rims (width) and I would recommend getting 195/65R(-) tires, if your vehicle body is stock. You can also go with low-profile tires for a wider setup but personally I wouldn't recommend that.
On my car, I have 6.5x14 rims with 195/65R14 tires. They look good and do the job without requiring any modifications.