Disc locks were invented by people who want to sell you new brake parts after you try riding off with your lock on the disk. If you're going to use one, here's my advice. Install it on the bottom of the disc, so that the wheel will not be able to rotate forwards. If you try to ride off, the bike will barely move at all. If you install the lock on the topside of the disc, the wheel will have almost a full rotation of travel to accellerate before the lock hits something and this will give it momentum to break things, like disk callipers.
Be aware that it's quite easy to bypass brake locks by unbolting the disc and using some straps to keep it in place. In the past I used an ABUS granit U-lock in the back wheel, which is considered the toughest out there, but I have nowhere to place it in the TR650, so I'm using this directly on the rear sprocket, and while riding I place it right above the left passenger peg. Not exactly Abus quality, but working well on the bike.
Disc locks just don't make any sense at all. If someone wants to steal the thing, they can carry it away between 2 or 3 of them....or lift the front onto a shopping trolley/skateboard / whatever and roll it away. Besides, everyone knows by now that you're royally rooted if you haven't got the right key to pass the EWS ...you'll never get the sucker running without it. Just lock the bike, pocket the key and pay for your comp insurance package...'cause nobody gives a &^% about any alarms going off, either.
