Road Clearance

Actually the 15" wheels and tires have maybe two tenths of an inch more clearance because the 195/65-15 tires are slightly larger in diameter than the 215/45-17 tires, depending on the tire manufacturer. But as you pointed out both sizes are listed at 5.5 inches ground clearance. Not very much but better than a lot of cars.

When mine arrives I'm going to go underneath and try to figure out what would get hit first.

 

The low point may be the bottom of a strut or shock tower at the wheels. Having read about the plastic panels covering the bottom to improve airflow, I looked under the vehicle today, and there really isn't anything lower than the black plastic that you can see at the front or rear edge of the vehicle.

The last assembly video in the following thread give you a good idea of the clearance.

http://priuschat.com/forums/gen-iii...2010-prius-made-in-tsutsimi-plant-videos.html

 

I'd have to believe the first thing that may be hit by a ground-level obstacle may be the front air dam.

Here's a photo of my then-3 week old '10 while installing a mod. I was shocked to see the scrapes on the lower edge. I swear it was not caused by me - very careful pulling up to curbs etc. Car had 5 miles when delivered - probably done during the final prep and testing at my dealer.

Pulling over standard sized curbs after parking, seems there's only an inch or so clearance.