[kedikedi]

Experiment results: my grinder was able to cut 18mm steel rod in about 20 seconds.

For completeness sake, I used a machinable steel rod, turned to 18mm. For cutting I used a Makita 18V grinder with a 125mm disc (I had a partially used disc. A full disc would cut it faster) and with a full battery (it cuts slightly slower as battery runs out).

[exodust]

Okay, but a proper experiment would use an actual bike lock attached to a bike, not clamped in a vice.

I have the Kryptonite New York Fahgettaboudit Mini. Two cuts are needed to remove it. Along with the quality of steel, and awkwardness of cutting a lock that isn't clamped in a vice, there's no way the thief will be done in 20 seconds.

The best seems to be the Hiplok D1000, which took 20 minutes for them to cut using a corded grinder, vice and several cutting blades. https://youtu.be/GMg6zVdYI0g?t=179

The Hiplok weighs 2kg, (same as my Kryptonite), so looks like a great lock for e-bikes. Only problem is, everyone wants one and not enough supply.