Originally Posted by
Banzai
Stem clamped to steerer tube below the expander plug insertion depth. Bad stuff...nothing reinforcing the inside of the clamp area. Given the length of protrusion, I don't believe that there are expander plugs that actually can insert that deep that the top cap will still be able to engage.
The only thing the expander plug (or star fangled nut) does is allow you to pull the fork assembly tight while you clamp the stem to the steerer. Once the stem is clamped, it provides the force necessary to hold the fork in place.
At no time should the expander plug be tightened so much that it requires a stem surrounding it to prevent the steerer tube from exploding!
Most manufacturers publish safety notes with CF steerers that specify how much steerer tube should protrude. Depending on the tube and the specs of the plug, it's either none, or up to about 1 cm. They are usually pretty specific about it too.
Not quite accurate... Most manufacturers publish two things: 1) the maximum allowed distance between the frame and the bottom of the stem, and 2) how far below the top of the stem the tube should be cut.
For safety, it's the first one that really matters. The second one only matters when the bike is being assembled: if the steerer extends too far above the top of the stem, you won't be able to pull the fork assembly tight. If you want to leave the steerer long, perhaps because you're trying to determine the exact size/placement of spacers underneath the stem, it is
common practice to stack spacers on top of the excess steerer tube. As long as the steerer tube ends slightly below the top of the last spacer, you'll usually then be able to pull the fork assembly tight enough to secure the stem. This is
not dangerous, provided you're smart enough not to over-tighten the expander cap to the point where the steerer tube explodes.