[Jeff Lee]

Assuming adequate tire & suspension, I believe it should be in the ballpark of 14 minimum.
Pending dyno results, I'm guessing my new or revised SS/H entry will have a 17.6 ratio (3.02 x 5.86). Automatic equipped cars may be less and it all depends on what engine you have. For example, I certainly wouldn't take something like a Pontiac torque monster to such extremes.
The new 2011 Mustang GT with manual 6-speed and optional 3.73 rear gears is 13.46 ratio! (3.61 low gear x 3.73 rear gear). I'm having a hard time understanding that, especially with a factory low aspect ratio tire on 19" rims...