drastically changes the handling of the bike, and not in a good way! Especially when said rack attaches to the seatpost. Usually when I get groceries things aren't nearly so heavy, but I had three half-gallon jugs of milk today and that's the main thing that increased the weight. It was an interesting trip home from Stop & Shop today--the load made the bike feel wobbly and top-heavy, to the point where I quickly decided standing up to climb was a very bad idea! Then things got even more interesting about 1/3 of the way home--all of a sudden I felt the load shift and heard a loud noise that sounded just like somebody on some sort of motorized scooter was right behind me (there wasn't anyone, and the sound turned out to be a strap from my backpack rubbing against the rear wheel); I pulled over and had to rearrange everything that was falling over and re-attach the bungee cords. However, I managed to get home without falling over or dropping anything, and was able to climb the steep hill on the way home without standing up or getting off to walk, so all in all it was a successful trip. Just thought people might find the incident amusing--I'm sure some of you have had your own!