I just did some Google Earth checking of Iron Mountain Road in SD. The sign on that road when you turn off of 244 says, "Large Vehicle Advisory" "Narrow Road Sharp Curves Ahead." And then a sign under that says "No Trucks."
I don't know about the rest of you, but that sign may not scare me away from the road. It doesn't say no RV's and there is no mention of a vertical clearance issue. There are signs like this all over California that I've drive my motorhome on without issue. Most two-lane mountains roads in California have similar signs.
