Replacement headset for Trek 5900. Great set of posts about the headsets in the 5900 vs the 5500s. A good discussion about the custom headset used in the 5900 frame that saves a few ounces and allows an a strong aluminum steerer rather than a carbon fiber one that will get destroyed if you over torque the stem bolt. Yikes, those things are delicate.
I've notice my own headset if pretty tight compared to say my buddies Cannondale CAAD7 with Campagnolo headset. Maybe the reason is this adjustment problem with their headsets which are apparently custom.
Mike Jacoubowski over at Chain Reaction Bicycles (the very first place I ever bought a bike 20 years ago!) says that you have to reinstall the lower bearings to get it smoother. Yikes, who knows how to do that. Maybe I need to call him. He says:
All you need to do is remove the fork, remove the lower bearing from the fork, reinstall the bearing and then reinstall the fork (with bearing attached). In 90% of the cases, that takes care of it. It doesn't seem to be a misaligned cup, but rather an issue with how the lower bearing seats in it.