Originally Posted by AslansMonkey
I believe you are talking about the hole at the bottom of the head tube. The problem with this hole is that it does NOT move with the fork assembly as the suspension flexes while the forks and tire themselves DO move. Brakes attached to this point will more than likely NOT be in alignment when applied, especially since they are likely aligned when no load is on the bike. Cantilever brakes, on the other hand, mount to the forks themselves which move WITH the tire and stay in alignment all the time.
It's also a bad idea to mount a fender using the hole at the bottom of the head tube as this will cause the fender to flex (since the struts are mounted to the dropouts, which move, and the center is mounted to the head tube hole, which doesn't) and break. Trust me on this one, I found out the hard way.
I just found this out today. I just got my springer mounted last night and went for ride this afternoon. When I tightened the spring bolt so it didn't rattle, the fender was too close to the tire.
I also noticed the movement on the caliper when the brakes were aplied. I'm OK with the brakes because it's still better than just the coaster brake.