I rarely pay those signs any mind. Once I’m out of the Bay Area, I can easily get away with 15 over (on Interstates marked at 70mph).
DW’s a little off on why they don’t race in the rain.
On ovals, they don’t run in the rain because it’s too dangerous (the walls are right at the edge of the track all the way around).
Everyone else runs in the rain on road courses. And rain racing is pretty interesting to watch; also the poor traction really separates the men from the boys.
Was workin’ +10-15 most of my trips also.