I see old thread, with new entries.
I'll have to look into that fork, I'm seeking a 20" fork to mount a disc. Long downhills heat up the rims enough to pop spokes.
In case not covered above, a couple things:
- For the same size disc rotor, larger wheels have more leverage. That means, if a rotor and caliper are designed for 26"/700c wheels, then put on 20" wheels, they are more prone to lockup, if they are powerful. The Dahon Formula 18 (discs) I test rode was very prone to lockup, especially the rear on a good downhill. Thus, good modulation is key. Hydraulics are best, but more complex maintenance issues. Maybe there's a sensitive mechanical caliper out there, or road discs have less grab. But a recent innovation is cable actuated hydraulic brakes, the cable pulls a hydraulic piston at the caliper, that sounds best of both words.
- There is considerable documentation online, regarding the risk of front disc brakes with conventional quick release axles, the brake torque will overcome friction and pull the axle out of the dropouts. They fixed this in back by mounting the rear caliper above the dropout, or inside the rear triangle; That is impossible in front, and you can't just swivel the caliper to the front of the fork (the disc slot will be on the wrong side); You could rotate it to the front, but then the cable would exit on the bottom. This is the impetus for thru-axles, that's why they were invented. Trek uses a "thru-skewer" (at least on their 520), requiring only a small mod to the fork. Some sort of tabs or rim at the dropout may help. Nutted axles may help. 20" wheels may help, as for the same ground-thrust, they are imparting less torque to the wheel system.