Scary...the 640 lock weighs 900 lbs!



Seriously, though, I am going to assume that they forgot to convert the grams for their European spec to lbs for the US site. Which means the 640 weighs 2 lb, while the 540 weighs 3.2 lb.

I think it boils down to whether 1) that 1.2 lb really matters to you, and 2) your comfort level with where you are locking it. Given that Abus locks are a lot less common than Kryptonite, I'm not sure a thief would distinguish between a 540 and 640 anyway. If they are going to take an angle grinder to the lock, we're probably only talking about 30 seconds or less difference anyway. Maybe the 540 resists jack-based attacks significantly better, but the real-world security between the two may not be much different. That said, I'd personally pay the weight penalty for the stronger lock. I have a 540 and would choose it again over the 640. Of course, I usually use it for my cargo bikes where weight is a non-issue.