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I'm looking for a bike lock and, in 2013, Kryptonite have a new lock, the Evolution Series 4 Mini Chain:

enter image description here

The chain is quoted as being only 55 cm long, and 10 mm thick.

Is the blue mark below a correct interpretation for the reported thickness?

Thickness of lock chain link


On that note:

To actually manage to remove the lock, would you have to cut through a single link completely in two places? See the red marked below:

Cutting the Kryptonite Evolution Mini Chain

If yes, then that would require cutting through 20 mm of manganese steel — exceeding the 18 mm thickness of the Kryptonite Fahgettaboudit that is often regarded as one of the best D-locks.

So when considering cutting, is the Evolution Mini Chain is actually more secure? (With the added benefit of being more flexible than a D-lock.)


On the other hand, if cut only once, would the chain link bend enough to allow the other to slip through?

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From a practical standpoint you'd need to cut all the way through one side of the link and at least halfway through the other. Cutting only one side would be sufficient if you had something to pry apart the chain, but doing so would be more tedious/time-consuming than cutting the other side (and would risk more damage to the bike). They could make things even more "interesting" by criss-crossing the fabric sleeve with steel wires which would tend to foul the cutting tool, but I'm guessing they didn't do that. –  Daniel R Hicks May 18 '13 at 21:50
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(In fact, they could make it really "interesting" by enclosing the chain in a gel which would foul a cutoff blade.) –  Daniel R Hicks May 18 '13 at 22:08
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Two cuts of 10mm diameter would be much easier than a single cut of 18mm diameter due to the reduced volume of material needing to be cut. –  Mac May 18 '13 at 23:00
    
@DanielRHicks That's a good idea... assuming the gel was thick enough and you couldn't bleed it out easily. –  Matt Jun 9 '13 at 23:04
    
another place to ask is insurance company. I remember they have a bike lock requirement when I tried to get a quote. –  imel96 Jun 10 '13 at 14:16

2 Answers 2

up vote 8 down vote accepted

As for the Kryptonite, cutting one side an bending is certainly possible, but in reality if you can cut one side, you use the same tools to cut the other. The tools needed to bend the link after cutting one side are almost certainly not portable, and why would you carry two tools when one will do.

In comparison to the D-lock - if you can cut though 18mm, you can cut through 20. It will make no difference. The main difference is a D-lock is susceptible to different tools to a chain. For real security - use both.

The reality is if they want it, is theirs, and the sweet nothing you can do about it. The job of your lock is to make you bike less desirable than the one next to it. If you bike is a $10K dream machine, that's going to be a tough job- you will need so much heavy metal it will weight more than the cheapest supermarket hack, and take so long to secure the time saving you get riding it is lost at each end of the journey. If its a $100 hack, then any half decent lock will be good enough.

The best you can do in reality is "enough to satisfy your insurance company".

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If one side of the D-lock is cut (e.g. the Fahgettaboudit), will it swivel around, or do you also need to cut it in two places? –  Baumr May 18 '13 at 22:45
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Even if it didn't swivel, you could cut it at the bottom of the "U" far from the shackle, from there, you could probably get enough leverage with your hands (or hands and feet) to bend it sufficiently to remove it from the bike. –  Kibbee May 19 '13 at 0:09
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And all of the added lock mass is a moot point if a thief can cut/bend/smash through whatever it is you're locking up to. (A good example are bike racks which are bolted to the ground.) –  WTHarper May 19 '13 at 4:27

As others have already explained, cutting through one 10 mm bit of metal is definitely easier than cutting through an 18 mm one.

In addition to that point the U-lock you use as a comparison would also require cuts on both sides as this video explains. This is basically because the locking mechanism locks both sides, and as you would need a massive tool to bend those 18 mm of steel you would really need to cut 18 mm × 2. And that makes it a much safer option than the chain.

PS: I just bought one of these u-locks so if I'm wrong please let me know!

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