This question has been plaguing me recently. Ever since I got my road bike I've been trying to stay on pavement as much as I can. I don't even ride on grass because I'm scared for my thin little tires that are so fragile-looking compared to the mountain bike tires that I'm used to using. Where should I draw the line with terrain that I should avoid on a road bike? A LBS guy once told me that he's gone down stairs on a road bike and it was perfectly fine!