Leaves, pine straw, gravel, how about ice. Seveal years ago I used to do a Christmas eve ride and a Christmas day rie and the same on new years. I pulled out of my garage on to my gravel drive and didn't notice the ice. I was down and sliding as soon as I hit the street. I managed to get stopped and back up on two wheels when the salt truck came by. I got my ride in and then went home for repairs to the body, fixed the bike later.