At last! Someone finally did a study on why shoelaces constantly come undone. This happens to me constantly and I've gone so far as to take out the worst lace culprits, the rounded laces, and put in flat laces. This helps but not 100 percent of the time.
"America’s epidemic of untied shoes can be blamed in part on faulty shoe-tying technique, according to rigorous experiments in a newly published study. But there is also a more insidious culprit: The mere act of walking loosens even a beautifully knotted lace and quickly leads to the grim fate the study’s authors call “catastrophic knot failure."
Yes, catastrophic, especially if you trip on the flailing lace or have to stop in the grocery store and bend over to retie them.
"Through a series of experiments, the team worked out the undoing of a shoelace. The downward spiral begins with the foot’s repeated impact against the ground, which loosens the central knot. Meanwhile, the leg’s swinging causes the lace’s free ends to whip around and gradually slide out of the knot. Finally, one lace end slips free, resulting in “runaway knot failure,” the researchers write in this week’s Proceedings of the Royal Society A: Mathematical and Physical Sciences."
The testing showed not all knots are equal. Shoelaces tied the conventional way, using the "bunny ears" technique taught to kids, failed every time they were tested at the maximum weight. The team labeled this the "weak knot." That's what I've always used. Here's an explanation of how to make a stronger knot, but my mind is such that I can't really picture how this works.
The weak knot is a version of the “granny knot,” made by crossing the left end of a piece of string over the right, pulling the left end through the resulting loop, and repeating. The researchers’ strong knot is a version of the “square knot,” made by crossing left over right as before but crossing right over left the second time.