Laces Keep Coming Undone: Cause and Solution

You tie your laces neatly in the morning and an hour later one of them is dragging along the ground again. If your laces keep coming undone, that is not bad luck. Researchers at UC Berkeley worked out exactly why a bow comes undone. The answer lies in the way you walk, the knot you tie and the lace itself. In this blog you will learn what happens and what you can do about it.

In short

• A bow comes undone through two forces together: the impact of your foot on the ground and the swing of your leg.
• The most common cause is a weak bow. You can recognise it by loops that point along the length of your shoe.
• Tie the first knot the other way round and a weak bow becomes a strong one.
• Smooth round laces slip out of the knot more easily than flat, oval or waxed laces.
• Laces that are too long give the bow extra work. Smaller loops or a shorter lace help.

What the UC Berkeley study showed

In 2017 Christopher Daily-Diamond, Christine Gregg and Oliver O’Reilly of UC Berkeley published a study on shoelaces that come undone. They filmed a runner on a treadmill with a slow-motion camera and tracked what happened to the bow. Two forces turned out to do the work together.

The first is the impact of your foot hitting the ground. On landing, the knot had to absorb an impact of about seven times the force of gravity. This makes the knot stretch slightly and relax again with every step. The second is the swing of your leg. As your leg moves forward, the loops and loose ends pull on the knot like small weights.

On their own, these forces were not enough. Stomping alone or swinging alone did not untie the bow. Together they made the knot loosen gradually, until it suddenly failed completely within a few strides. That is why a lace often seems to come undone out of nowhere.

Why do your laces keep coming undone?

Usually because of a weak bow. The researchers also compared two ways of tying that look almost identical. The strong bow is based on the square knot, also known as the reef knot. The weak bow is based on the granny knot. In the tests the weak version came undone far more often. A strong bow can eventually come loose as well, but it holds out much longer.

You can see which one you tie by looking at your shoe. If the loops sit across the shoe, from left to right, you have a strong bow. If the loops twist lengthwise, with one loop pointing at your toes and one at your ankle, it is the weak version.

The fix takes no extra time. All you need to do is tie the first knot the other way around. If you now cross the left end over the right, cross the right end over the left from now on. Then make the loop and wrap the lace around it as you are used to. If that does not work for you, you can also wrap the lace around the loop in the opposite direction. Either change turns the weak bow into a strong bow.

Other causes and what to do about them

Cause	How to spot it	Solution
Weak bow	Loops point along the length of the shoe	Tie the first knot the other way around
Slippery lace	Shiny synthetic cord, bow slips while you tighten it	Choose a flat, oval or waxed lace
Lace too long	Big loops and ends that almost touch the ground	Smaller loops, a double knot or a shorter lace
Knot too loose	Bow already feels slack before you start walking	Pull both loops tight after tying

Slippery or round laces

The smoother the lace, the less friction there is in the knot. A smooth round cord made of synthetic material slides easily through the eyelets, but also slides easily out of a bow. Flat laces have more contact in the knot and stay tied better. Oval laces sit in between: they tighten smoothly and hold the knot better than a round cord.

Waxed laces

A wax coating gives the lace extra grip in the knot. That is why a bow tied with a waxed lace stays put noticeably better. For sneakers and casual shoes, choose waxed laces of 8 mm. For dress shoes there are waxed round laces of 3 mm, which also fit small eyelets.

Laces that are too long

The study shows that the swinging loops and ends pull on the knot. The longer they are, the more there is to swing. A lace that is far too long for your shoe therefore gives the bow extra work. Make the loops smaller or tie a double knot. If it keeps happening, choose a shorter lace. Our shoelace length guide shows which length suits your shoe.

A double knot

A double knot holds better, because the loops are tied together once more. The downside is that it is harder to undo and uses extra lace. So tie a strong bow first. Often you will no longer need the double knot. For sport or kids shoes it is still a good extra safeguard.

Frequently asked questions

Why does one lace come undone and the other does not?

You usually tie both shoes the same way, but pull one bow less tight. A small shift in the first knot can also turn a strong bow into a weak one. On the shoe that keeps coming undone, check whether the loops sit across the shoe.

Do new laces help against coming undone?

Yes, if your old laces are smooth or worn. A flat, oval or waxed lace has more grip in the knot. A new lace will not fix a weak bow, though. So make sure the first knot is right too.

Do laces come undone faster when running than when walking?

Yes. When running your foot lands harder and your leg swings faster. According to the study, those are exactly the two forces that untie a bow.

Is a double knot bad for your laces?

No, but if you keep yanking it open, your laces will wear faster. So always undo a double knot before you take off your shoe.

Looking for laces with more grip? Browse every shape and material under laces by type.

Source: Daily-Diamond, C.A., Gregg, C.E. and O’Reilly, O.M. (2017). The roles of impact and inertia in the failure of a shoelace knot. Proceedings of the Royal Society A.