Originally Posted by
mtseymour
Welcome to the site!
The BB7 was designed for single bikes, and it has largely fallen out of favor due to far better designs. It's rare to find the BB7 on new single bikes (mid to high-end) due to its single piston design. The BB7 uses one piston to push a pad against the rotor until it flexes against a fixed pad. It's difficult to setup the BB7 to be quiet and provide enough braking power for steep descents. The constant rubbing may explain your warped rotor.
By comparison, the TRP Hy/Rd and Shimano R785 hydraulic brakes use dual pistons to squeeze the rotor from both sides. They're quiet and are powerful enough to long, steep descents (8-12%). The Hy/Rd should be compatible with your Shimano 105 shifters, while the R785 brakes will require new shifters. Check with Co-Motion to see if the Mocha rear triangle can handle a hydraulic brake. If your team weight is around 300 lbs, you can probably use 180mm rotors with the R785.
In our experience, the Hy/Rd and R785 are substantially better than the BB7, regardless of the pad or rotor combination. If the BB7 is not good enough for a 170lb rider on a single bike, why use it for a 300lb tandem team?
Going "full hydro" with road setup means giving up the triple chainring, I'm pretty sure, and converting to 11-speed (assuming your bike is 10-speed as is stock on comotion), a very big expense requiring replacing shifters and all the drive train parts. If you have flat bars you dont have to deal with all that. The Hy/Rd are cable actuated hydraulic, with the reservoir at the disc, so you dont need to replace any shifters or drive train parts.
I have no experience with Hy/Rd, but the Spyre also are dual piston activated. I converted from the BB7. In my experience the BB7 were almost as good in comparison. With the 200mm rotors used on tandems it takes very little force for the single piston deflect the disc slightly so that it contacts the pad on the other side, so the dual piston actuation does not yield major improvement in stopping power. I also did not have problems setting them up without rubbing, though the dual piston is easier to adjust.
My brake experiment is ongoing. I expect compressionless housing and the Ice Tech rotor for the rear any day in the mail. So far have been underwhelmed by the stopping power, but it is adequate. My main thing is heat dissipation as we ride a lot on long steep gravel descents.