[albrewer]

I had a similar experience but had an opposite takeaway. I learned that my car, in dry, daylight conditions, could comfortably go 20±5 mph faster around curves than those signs suggest.

[542354234235]

Those signs aren’t just for whether you can go around a curve comfortably. It is if you can see and/or stop safely if something happens. If there is a broken-down car in the lane, you will see it way off at 65 mph, but if you are going around a blind curve comfortably at 65 you might plow into it or skid off the road.

[IIsi50MHz]

Those signs can also be posted as advice for adverse conditions like snow and rain. (Of course, ice = all bets off)