I've just bought my first expensive (€820) bike and I am now concerned about the security of bike locks. I have cycled for many years and originally used only a cheap U-lock, after loosing a rear wheel I then augmented it with a cheap cable lock and would lock frame+front wheel with the U-lock and then the cable to lock the rear wheel and that has worked fine for many years, however the key point is probably that all my previous bikes were not really work stealing (<€300 new). So with the new bike I did buy and additional Kryptonite U-lock (https://www.amazon.com/Kryptonite-Evo...ef=pd_sim_sg_9). Now I have 3 locks but I'm concerned that the existing cable lock (and possibly the existing U-lock) might present no challenge to a thief. They did have locks rated up to 15 (vs 9 for my new kryptonite lock) but my problem with these is that they weigh so much. The bike was so expensive because I chose the lightest components so I don't want to negate all this by then saddling myself with an unbreakable lock which weighs half as much as the bike itself.
One option which looks promising is these kryptonite cables which can be used in conjunction with the U-lock (https://www.amazon.co.uk/Kryptonite-K...4184054&sr=1-4). Does anyone know if these are any good or might they be just as crappy as my existing cable lock ? Is there any independent measure of how secure locks are relative to one another ? Anyone have any other suggestions bearing in mind that I want best protection for a minimum weight ?

Where are you locking up your bike? and for how long?

Yes a solid steel U lock and a meter of hardened steel chain will be heavy.
worth it to not have your bike Nicked, your call ..

I recommend the type of chain with the links made out of square steel,
they are harder to cut with bolt cutters, than common chain made out of round steel,
and I recommend that over any cable used to lock up your bike

I use a Ring Lock, AXA defender and the lighter 1.4m chain that they make to combine with the wheel lock
attached to the frame.

But Im not in a high theft city , and I have solid stuff to lock my bike too ..

Cables only for quick trips into the shops, secured by Padlocks..

No such thing as an unbreakable lock, unfortunately. Even the toughest U-lock will fail under an angle grinder, and the thickest cables and chains can be severed by bolt cutters if the cutters are long enough.

Still, no one ever regrets having too much lock, just too little. I like being better locked up than the bikes around me, with the thought that thieves will pass up my bike for an easier target. No matter how much lock you carry, don't leave a nice bike in a high theft area and expect it to be there when you get back. If you must leave a bike in these areas, ride your beater.

It's said that all secure bikes weigh 50 lbs; 20 lb bikes require 30 lbs of lock, 40 lb bikes require 10 lbs of lock, and 50 lb bikes require no lock at all.

Locking up properly is really important. Having a bike stolen totally sucks.
Here is some good concise info on the different kinds of lock out there.

As noted, any lock can be defeated. The goal is to use a lock sufficiently tough so that it will:
1. Take too much time.
or:
2. Attract too much attention.

So, it's not only what you use to secure your bike, it's where and to what. Although angle grinders and huge bolt cutters are effective, they require a bit of privacy... Most thieves don't want to carry around a three-foot set of bolt cutters that weighs 25 pounds, and grinders make a lot of racket and throw sparks all over.
In fact, in my (considerable) experience, the vast majority of bikes that are stolen are mid-level mountain bikes that are secured with cables.
The cables are easily cut with a very small bolt cutter, and the bikes can be quickly pawned or sold.

High-end bikes are harder to move; pawn shops are generally not interested, and the local crack dealer isn't either.
In certain areas, there is sophisticated traffic in high-end machinery; even to the extent of re-stamping or altering serial numbers and such.
That's unusual, though.
We give the students a discounted Kryptonite lock, and over the many years we've been doing this I can count on one hand how many of these have been defeated.
The many bikes we do get stolen are almost all secured with cable locks.

Your bike only has to be harder to steal than the bike parked next to it.

other suggestions - Search the boards for the many discussions. Without being preachy, Why do you own a piece of property you cannot afford to lose? I personally suggest taking the seat post with you. You can also buy a cheaper or used wheel set for commuting purposes. You can also buy an engraver and engrave your name on all parts making the bike worthless. A GPS tracker bug with SMS messaging may be worth investigating.

My favorites are here:

https://simplecycle-marc.blogspot.com...ore-locks.html

Marc

One point I'm always amazed at is Bicycle Locks, my last stolen bicycle was at a San Franciso Bay area BART station in 1976, very nice Schwinn Super Sport I wish I had again.

We pay all this money to get the lightest/greatest bicycle, then we have to weight it down with heavy locks, sort of defeats the purpose...

Now I need to consider buying a U-Lock, don't have one at the moment.

If the weight of a lock is a concern, you may be able to leave the lock behind, locked up.
If you are commuting, have a lock at both ends that you leave in place.

No lock is more secure than what it is locked to.

Just pointing out that most of the time bikes are at best locked to a post of soft iron.

And once a bike is in the shop no lock is going to hold up to a cutting torch.

Those Kryptonite cables will get defeated quickly with almost any bolt cutters of decent length. Maybe you can just get a beater bike for when you want to lock your bike up and use your nice bike and never lock it up. That's what I do. Seems to work so far. I still carry a cable lock anyways, but only to lock my nicer bikes up to the bus rack if I get stranded from a flat. My nice bikes never get locked up outside. Too precious for me. If I had to lock my bike up all the time, I'd just get a folding bike and bring it inside everywhere.