Originally Posted by
aliasfox
I think this may be the first time I've heard that 'excess steerer length must be cut,' as I've always read that the top of a carbon steerer tube should stick out slightly (5-10mm) to avoid crimping the top of the tube.
You want a small amount of excess height - a couple of mm - but you don't want a lot, just enough to hold a short spacer in place. You don't want the steerer to extend further beyond the headset than the maximum height the manufacturer recommends, and you usually want the expansion plug to be centered in the same area of the steerer where the stem is clamped, so unless you have a long extension on the expansion plug you're limited in how much steerer you can leave above the stem.