The fatal flaw of bike locks: Freezing one makes it easy to bust open. Check out video of some DIY bike theft inside.
Posted 09.24.2012 at 10:09 am
12 Comments
Stone-Cold Lock
This U-lock was specially treated to make it harder to break. But after cooling it with canned air, it cracked with just a few blows.
Mike Walker
Strong, hard, tough. These sound like different ways of saying the same thing, perhaps describing a really good suitcase. But when applied to the physical properties of materials, each of these words has a very specific technical meaning that distinguishes it from the others. And those definitions explain why it’s so difficult to make a bicycle lock that can foil thieves.
Imagine a chain made of diamond. It would be impossible to cut with any hacksaw, but it could easily be defeated with a brick. Diamond is hard, but also brittle, much like glass. What diamond lacks is toughness: the ability to absorb energy without failing. A chain made of rubber would be far tougher in the technical sense. You could pound it for hours with a brick without breaking it. But it would not be hard enough to resist cutting.
Hard vs. Tough: At room temperature, a rubber ball is soft but tough and resists hammer blows. At –321°F it’s rock hard and cracks easily. Click here to see this amazing image even larger. Mike Walker
It’s actually not possible to make the hardest material also very tough. Harder materials can’t yield to absorb energy and then spring back the way softer ones can. Their hardness means it requires less energy to break them. Take steel, for example. Bike-lock cables are made of very tough steel. You can’t easily break a cable by hammering it. But compared with the high-carbon steel used to make tools, it’s very soft, so it can be cut with a hacksaw.
Good locks are case-hardened, which means they have a hard but brittle outer layer protecting a tougher, softer inner core. But savvy thieves know that even good locks have a fatal flaw: Nearly any material, including steel, becomes less flexible when it’s very cold. Although it doesn’t lose any tensile strength—defined as how much force is needed to break it—the loss of flexibility makes it less tough.
When cooled to –13°F with canned air spray (actually the compressed chemical difluoroethane), even very tough locks become brittle enough to smash open with a hammer. So there isn’t much that lock manufacturers can do to finally put an end to their long war with bike thieves. In the meantime, you might consider just taking your bike inside with you.
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How come almost every time I try to watch one of the embedded videos on this site, it fails for some reason. It's either removed from youtube or it just fails or something. Always some reason...
My bicycle lock and chain is covered with 1/3" thick pad of cloth made of nomex, neoprene, cotton and kevlar.
I made it because I didn't want the lock to rust, Also, sometimes I park my bike in the sun which makes it really freakin'hot.
One day, I found the cloth around the lock feeling wet, cold and partially ripped. Now I understand why! Thank you Popsci. I didn't know I invented something theft resistant! :)
Okay, I have had 3 bikes stolen in my day. I really appreciate this responsible journalism. Now I too can use science and go get some bikes (only to replace my stolen bikes I promise. This tech will not be used for capital gain)
Cool information to help the public. Not so cool for the lock, in illustration of its fragility via it being extra cooled.
This method has been around for a while, but really a cordless 4-inch angle grinder with a metal blade will go through a Kryptonite in about 3 seconds. I know because I used one to get my bike free after I had lost the last key, and because the locksmith wanted to charge me 90 bucks to cut it with a Dremel. I rented the grinder for 11 dollars for one hour at Home Depot. FYI...and yes your bike will be stolen if someone wants it bad enough. I had a $900 Cycle Craft cruiser stolen from my friends wake here in Austin,TX.
Lame... the canned air didn't bring down the temp of the steel enough to smash it. Only after an off camera dip in some liquid nitrogen was the lock able to be compromised. Don't worry, thieves are not going to be carrying around pails of liquid nitrogen just to steal a bike. I'm sure they'd be using it to smash something more valuable. Considering what a headache it is to obtain liquid nitrogen in the first place, AND handle it safely.
To achieve the best results with canned air spray, hold the bottle upside down. Also, I hear that rubbing alcohol poured into a cup with dry ice gets real cold (dangerous though, don't touch it because it will stick to you). Cold enough to smash a lock? I dunno. Anyway Liqued Nitrogen.. you can't just buy it unless you go through some sort of formal process I think. Anyway I just thought I'd put that out there...
This is total BS.
And even if it isn't, when do you have a bike lock in a position on a work bench the way they show it so you can easily freeze the lock and then hit it with a hammer ?
Never ?
I had a krypto lock I lost the key for, and mind you, this is like 20 years ago. I bought freon, froze the lock, and blasted it with a hammer: Nothing !
And here I should note, I've worked as a carpenter so I know how to swing a hammer.
Thought I'd done something wrong and so bought a second can and had a friend come with me, he emptied the can on the lock and I immediately went to work with the hammer, and again NOTHING !
I hit the lock until it began to damage the frame of the bike.
PopSci = fail
It works on those silly steering wheel locks too!
www.AnonNation.tk
I would be faster and quieter just to pick the lock.
Those crappy ulocks I can pick in less than 10 seconds.
Back in high school I made and sold a little lock spinner.
with just a couple of twists you could open any cylinder lock.
For the less skilled you can even pick those locks with a bic pin..
www.youtube.com/watch?v=3bosEh5PUNs
i worked in bicycle shops for years and this is one of those things we had all heard of but none of us had ever personally dealt with.to me the problem with stealing a bike this way is the destructive nature of using a hammer as a lock pick.the force has to go somewhere and the u lock is wrapped around the hollow tubing of the bicycle as well as what it's locked to so all it takes is one mistake and the bicycle is ruined.plus it means buying the freezing agent and carrying around a hammer and then trying to do all that stuff on a street corner without anyone noticing.good luck. sonnygrunt is right. you can do this with a 50 dollar cordless angle grinder from home depot and you can do it in a count to five.
in my experience most bicycles are stolen from peoples' yards and garages with the occasional act of carelessness thrown in.your best bet is to lock it on a busy street and endeavor to bring it in at night.i don't know who to attribute this quote to; "locks only keep the honest people out."
All of you are missing the point. This article is not about stealing bikes. It is about the difference between hardness and toughness. Two words that mean different things, but are often used interchangeably.