The 2-piece red rotor in my previous post is a Formula, which I purchased from UniversalCycles.com. I purchased front and rear kits, which came with their respective adapters. However, last I checked, the 220mm rear adapters were no longer listed. Universal is usually good about listing out-of-stock inventory with an "expected by" date, leading me to wonder if the rear adapter has been discontinued. Perhaps an email to Formula USA would be in order.
Alex at MTBTandems reported receiving some Hayes 224mm rotors shortly after they began shipping. Drop him a line to check his stock.
The rear Formula rotor in the photo I never used, though I have a matching one up front. At the rear, I just completed a Speedhub conversion on this bike, and ordered a Hope custom 220mm with a Rohloff 4-bolt mounting pattern, though conventional 6-bolts are an option. Visit HopeTech.com and drop them an email for ordering information.
We had our inagural ride on it last night, and the Hope performed well. Hope only has the capability to cut 1.8mm rotors, something they blindsided me with after I received my rotor, so it remains to be seen whether this option will stand up to tandem abuse.
It's natural a manufacturer would stipulate you only use their rotors with their calipers, if not for liability, then for sales. However, I've never had a problem mixing and matching other makers' rotors with Avid BB7s, which are single-sided actuated and therefore "push" the rotor into the opposite-side fixed pad. If it's not a problem with these brakes, I can't imagine it being an issue with 2-piston calipers. My list of other-brand rotors includes stout 165mm x 2.0mm Magura units sold by Rohloff, and the Avid calipers have no problem flexing them sideways.
Good luck with your search!
