Kryptonite Evolution Series 4 Bicycle Disc Bike Lock - Heavy Duty Anti-Theft U Lock for Road & Mountain Bikes - Secure Your Bike in High Crime Areas (Red)

This is an awesome disc lock for motorcycles! It's small enough to be carried around easily, but burly enough to look and feel solid when locked on the bike. I use it to attach my chain to the bike in bad parts of town, and I also use it just by itself when I'm on the go and don't want to carry a chain. I like the yellow color because it's bright enough to act as a deterrent, in addition to making my bike more of a pain in the rear to steal. It comes with three keys (one lighted) and all work great, plus it has a unique serial number so you can have new keys made in case these are lost. The lock mechanism is smooth and easily accessible (a BIG plus if you've ever messed with disc locks before) and I just lube it every couple weeks and it been quiet and efficient. The shackle is nice and wide, so it will fit around most discs on most bikes and still have space to add a chain, but its also very thick (good for resisting cutting) but trouble if your disc has only small holes in it. That being said, I can also throw this around the rear sprocket with no issues, and the rubber coating is nice and protective so it doesn't damage the bike.This has become something I use several times a day and love it so far, I will update this review if issues arise in the future.