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Nowadays there are so many different high-tech materials, so I wonder if there is a suitable material for bicycle locks that would be much less heavy than hardened steel. If there isn't one, can somebody explain from the perspective of materials science why?

The only non-steel material used in locks that I could find is Kevlar, but mostly just as a coating around steel, and from various reviews I don't get the impression that they are better or lighter than ordinary steel ones. My understanding is that kevlar has good tensile strength (so gun bullets can't tear kevlar fabric) but it doesn't resist being sawn or cut. Carbon fibres would presumably have similar issues, it's fairly easy to damage carbon frames if you compress them so a potential carbon fibre lock wouldn't resist bolt cutters.

So are there any light materials that would have the correct properties for a bike lock? And if not, why not?

  • 1
    I use the lightest bicycle security mechanism of all. Eyes. Never let your bike out of your sight. – andy256 Jul 7 '16 at 23:36
  • There's a 560-gram (1.23-lb) folding lock on kickstarter made out of titanium. It's marketed as lighter than other "high-security" locks, but the early-bird price was $150. Ouch! kickstarter.com/projects/1282151086/560g/description – Nick Weinberg Jul 8 '16 at 2:43
  • For more expensive (and often lighter) bikes, securing the peripherals (saddle, seatpost, handlebars, brakes/shifters, etc.) is also an issue. – Craig Hicks Jul 8 '16 at 2:52
  • @NickWeinberg Don't trust kickstarter advertising. I remember seeing one titanium lock that was "uncuttable by bolt cutters" until someone tried and it cut easily with some short 300mm bolties. $150 is more than my bike cost! – Criggie Jul 8 '16 at 8:42
  • J&B brand Sunlite makes an aluminum U lock, it is very light compared to others but is meant for low crime areas only as it would not be hard to cut. – Nate W Jan 26 '17 at 22:50
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There isn't all that much point.

We have a lot of knowledge on how to make steel tough. It's also pretty cheap. This basically makes it win-win for manufacturers: use enough tough steel in a good structure with a good locking mechanism to get a decent lock. It doesn't cost a lot and its easy to fabricate.

The weight of many good locks is not that much to begin with; the main design goals with a U-lock is to leave as little space as possible to get a jack in, hard enough to cut, and has a proper lock mechanism. So, locks like the Kryptonite Evo Mini line are very good for many locking jobs and don't weigh all that much (about 1.5 lbs for the Mini 6). So, there's not all that much point in reducing weight.

There are some locks which are not steel -- Tigr makes titanium locks, for example. But they're less well known and twice the price of a high quality steel lock, such the well tested Kryptonite New York Lock line. And the smaller units don't necessarily hold up.

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    Another issue is that part of the defence of a lock is size - a fatter lock part needs a bigger tool to go round it, or requires more material be cut away to sever it. – Móż Jul 7 '16 at 23:04
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    There are some lighter material locks out there, i believe there are even aluminum alloy composites but you sacrifice strength for it being light. The ones i have seen even say they are for low crime areas only, So i doubt they would hold up if someone tried to break one. Sunlite (J&B Brand) makes a mini U that is less than a pound. – Nate W Jul 7 '16 at 23:10
  • Indeed there are others, but I'm not convinced of the quality of the Sunlite ones. – Batman Jul 7 '16 at 23:52
  • Weight is relative. The frame on my sturdy steel Surly Crosscheck weighs 3 lbs. – Craig Hicks Jul 8 '16 at 2:54
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    Seems like an underestimate (JensonUSA seems to say frame+fork is around 7 lbs for a 56cm) but if you look at the complete bike its about 25 lbs according to bike radar. Adding in a 100 pound rider, its about 2% of the weight of bike+rider. And most people will by 2 pounds each day anyway. – Batman Jul 8 '16 at 3:01
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The challenge is to prevent the lock from being cut or pried open. Standard steel locks do this by using a steel bar, cable, or chain that resists bolt cutters and abrasive wheels due simply to the strength and hardness of the steel.

However, one can also prevent the lock from being cut by "frustrating" the cutting process somehow. For instance, a cable which flattens and mushes around when you attempt to use bolt cutters on it will be harder to cut. And a lock bar or cable which somehow contains materials that foul abrasive blades will frustrate the standard angle grinder type cutter. A single approach would not be sufficient to protect against most attacks, but a combination of several "frustrating" technologies would probably work (and possibly be lighter than the conventional lock).

But, to my knowledge, no one has attempted to market such a lock.

Update: There recently was a lock introduced which sorta does the above. It's U-lock where the "U" contains a nasty liquid which is supposedly non-toxic but which makes you vomit. Anyone trying to cut through the "U" would be in for a nasty surprise.

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    "which somehow contains materials that foul abrasive blades" - interesting idea! industrial grade diamond is priced at about $2 a gram. – Craig Hicks Jul 8 '16 at 2:48
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I redesigned an Electric cattle prod, fitted it under my seat, wired it to the bike frame. It is remotely armed and at discharge it releases 70000 volts at 4 amps. It is very effective. It has already knocked one person out and stunned another when they tried to steal my bike. I still use a normal $30 lock and don't arm the shocker in safe places but if I am visiting out of area I do arm it. So far I have still got my bike and will defend it with their lives if I have to.

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    Well, that would probably be illegal at least in Europe (don't know about other countries). What if your friendly elderly neighbour comes along, thinks he'd take the bike inside so that it doesn't get stolen, and has a heart attack? – Stephan Matthiesen Jul 9 '16 at 7:43
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    This sounds like a bad idea in all possible ways, legally, ethically, morally, and physically. – Criggie Jul 9 '16 at 9:55
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    I'm not sure I believe you because there are so many reasons a bike may be touched besides intention of theft. Mostly other people locking or unlocking their bikes in the vicinity of yours. But it could also be a 3 year old kid who thinks your bike is so cool and before mother can react the kid has touched the bike. The liability you would expose yourself to - that would be a real "shocker". Compared to that losing your bike would be peanuts. – Craig Hicks Jul 10 '16 at 4:27
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    I'm pretty sure that's illegal in the US, too. – Batman Jan 26 '17 at 23:08
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    Someone with a pacemaker or weak heart could be killed simply by brushing your bike accidentally. You are essentially behaving like a sociopath. – Rider_X Jan 27 '17 at 18:18

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