Originally Posted by LukasM
If you want to save some money you can also get a cheap axial MC with 13-16mm bore from a street bike (if using a 4 or 6 piston caliper). And the Motomaster caliper is actually designed for use with 11-12mm dirt bike MCs so it has 4 smaller pistons and works very well with a standard KTM Brembo.
The budget alternative for calipers is the gold 4 piston Brembo that is used on the KTM Dukes, 640 Supermoto and some Ducatis. It has good stopping power, and huge selection of pads, and it can be used with 4mm or 5mm discs, but it's fairly wide and needs a special caliper bracket and disc spacer to make it work on the standard EXC forks. Here is what it looks like mounted, if you need help finding a caliper, I've got a spare I'd sell cheap.
What about for those of us who don't want to deal with the hassles associated with swapping-out caliper adapters and all that stuff? Running a 19/17 Woodys wheelset and wouldn't mind having a little more braking power on the street, but don't want to run a bigger rotor on my dirt wheelset.