I just received a built up wheel with a Powertap hub.
I tried to put my own (Ultegra 10-speed) cassette on it, but when I tighten down the lockring, there's still too much space between the last gear and the base of the hub, so the whole cassette doesn't tighten down.
This isn't a torque problem - even when torqued down appropriately, there's about .020" (about half a millimeter) too much space between the hub shoulder and the smallest gear.
What gives? Am I missing a shim? The hub just isn't compatible? Something else?