Originally Posted by
f4rrest
When you look into the top with the 2 spacers on top as you posted, you can clearly see the gap between the top of the 2nd spacer and the top of the steerer tube. Some gap is necessary to establish tension bearing preload when you put the cap on, but this gap is already a bit large:
Now, when you put the spacers back under the stem, the gap is between the top of the stem and the top of the steerer tube. If you add the 3rd spacer under the stem, it simply makes that gap taller -- in your case, it's dangerously taller since it pushes the top of the steerer below the highest clamp bold. I wouldn't ride it like this.
^ This seems to make sense.
Consider the stem to be a very tall spacer. It can hide the actual height difference between the steerer tube and the stem+spacer stack. The danger is that the stem needs to clamp more steerer tube than less. I have started cutting my steerer tubes too long on purpose so I need to use a spacer above my stem. This way I know that the stem is clamping 100% steerer tube.
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