What is the lightest chain lock that would present difficulty for bolt cutters?

Question

I was told in a bike shop the other day that the Kryptonite Keeper 785 chain has been tested and can’t be broken with a bolt cutter.

I was really looking forward to getting one of these because at the moment I’ve been using a similar motorbike chain from eBay except that it’s 1.8m and quite heavy.

Miraculously by looping it through my frame and both locks it’s done the trick. However the other day some stupid station staff dealt with it using bolt cutters and dumped it on the side of the road. This made me think that I really need to get something better.

I posed this question to the keeper of my local chain bike shop, who assured me that the Keeper 785 was heat treated and wouldn’t be cuttable without an angle grinder.

I then went price shopping for one online and found a review that seemed to suggest that those indications of its bolt cutter resistance on YouTube were deceptive.

This solution combined with pit locks was going to be really appealing to me, because I normally hang the chain around my neck and behind my back whilst I’m riding, although the 1.8m one is a really heavy burden. Being told that the 1.5kg keeper would do the job and hang neatly around my neck like a necklace made my day.

I also don’t like carrying stuff so a d lock would be pretty awful.

However, if this unfavourable review is right, then what would be my options?

Answer 1

Per se, the question is a product recommendation, that is off-topic here. So I won't answer it directly. Also, the question also contains some contradictory elements, as a good lock needs to be heavy, and the answer lies in where you choose to place the cursor in the compromise "weight"/"thoughness". I would also not focus on the tool needed to defeat the lock (an portable angle grinder is easier to conceal than a bolt cutter for instance).

But there is an implicit question, that is linked to the convenience of carrying the lock.

If you don't want to carry stuff, then the solution is to find a lock that you can mount on the bike itself.

If you don't want to clamp the lock mount on your frame:

• folding locks mounts can be attached on bottle cage mounts (but not the heaviest ones, and they are known to be "easier" to defeat than u-locks).
• U-locks mounts can also be mounted on seat posts (maybe an option given you are tall enough, but that depends on the combination lock and mount here, given seat posts can be replaced, it will leave your frame intact but may not work for all seat posts).
• you can also fit a rack
• another option would be a seatpost mounted rack (see picture below). It the point is only to carry the lock, you can take one with a (re)movable platform, and use the beam as mounting point for any lock mount.

Answer 2

Any lock can be defeated by a determined thief. My goal is to make my bike such a PIA that a thief will pick another bike to take. I use a serious U-lock, folding lock, and a disk brake alarm lock. The U-lock is my primary lock and the others are secondary, but I use them all together. You could substitute a chain for the U-lock or use both a chain and a U-lock plus a disk lock alarm. I can fit all three into a backpack, on the bike, of a mix of attachments and backpack. Good luck.