I have a cargo bike equipped with a Nexus 3 hub shifter and related roller brake. Since where I live is pretty hilly, I'd like to replace it with a shifter with a big range and little gap between the gears, as the 11 speed Alfine hub shifter. Unfortunately, the Alfine is available only in disk version, while my bike doesn't have mounts for disk or v-brakes. Moreover, the bicycle has poor braking performance when fully loaded, so a disk brake would be a valuable addition.
Is there any adapter I can use to mount a disk brake caliper on the rollerbrake mount? Are there chances that the bike present clearance problems while trying to mount a disk brake on it?
Update: In the end I mounted a Nexus 8 shifter with its own brake. The rollerbrake sold with the nexus 8 is the one with heatsink fins and, after some months of use, I can say it offers a lot more braking force than the one that comes with Nexus 3. The braking performance of the rear wheel is now comparable with a good disk brake (with less, but overall sufficient modulation). Adding the proper braking grease increase the modulation. I can warmly recommend this setup to anyone has similar constraints.