Go to
http://www.tirerack.com enter your tire size, and pick any tire.
Click on "specs". You'll see every size for that tire.
Look at tire "overall diameter", and "rim width range".
Stay within 1" OD of your factory tires, and a width that fits your rims.
Your 185/65r15 is 24.5" OD with 5.5" rim width. I'm using 195/65r15 with 25" OD with 5.5"-7" width range. My speedo error is 2 mph slow at 70 mph. (GPS/OBD speed)
BTW the sidewall bulge protects my rims from road rash.
TireRack has loads of good Info. Buy tires anywhere you choose.