The first time I drove in the US I came up to a turn with the yellow speed sign. I was going faster and I could feel my car strain to not go off the road. This is to this day the second scariest thing I've experienced in a car.
After that I 100% followed the yellow signs.
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.
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.
Those signs can also be posted as advice for adverse conditions like snow and rain. (Of course, ice = all bets off)
> This is to this day the second scariest thing I've experienced in a car.
I have to know! What was the scariest thing?
Going past a line of cars that were backed up and going like ~10 km/h and some guy in a pickup truck suddenly decided to force his way into the line and hit a car so it jumped into my lane by a meter or so. Only time I have ever needed to perform the moose maneuver we are taught in driving school :P
I was lucky there was no car in the lane to my right.
Oof!
Here are my two scariest recent ones...
I was driving north on Highway 87 in San Jose in the #2 lane (second lane from the left) when directly in front of me was a big metal rack, standing up in the road! It looked like something you might hang clothes hangers on. Which made it all the worse because it wasn't as visible as a heavier rack.
I hit the brakes and swerved into the #1 lane to avoid it. Luckily no one was in that lane. I try to keep situational awareness of the lanes to my right and left, so I felt pretty sure that no one was in that lane next to me.
The other was driving on northbound El Camino in Menlo Park, in the rightmost lane, at night.
Someone was riding a bike in that lane, dressed all in black (and even a black hoodie), with no lights or reflectors or anything to make himself visible. And he was doing that thing that some young people like to do where they weave back and forth for no reason at all except that it's fun?
Another brake slam and swerve to avoid him. It ended OK but was definitely a white knuckle moment!