When I was a kid I had an old Schwinn, big tires, no gears... what do you call those? Anyway, I used to see if I could ride on the curb for a block without going into the gutter or into the park strip.. was lots of fun, but I don't remember ever running into slippery curbs. I can see how they might be slippery when they have several coats of paint on them and are water wet though.. I assume you mean wet with rain, not wet from being painted?