My Moots Vamoots RSL uses a 5mm spacer under the stem camp, since my local bike shop (LBS) claims it is necessary for the integrity of carbon fiber steerer tube.
The concern arises in part from failure of Trek steerer tubes, at least that is where I understand the basis comes from.
As is the case with any oddball failure, urban legend builds up from specific failure cases of specific brands (or even batches of parts) to generalizations that might or might not be true, be it bicycles or cars or anything else.
My understanding is that most forks are now strongly reinforced inside the top end of the steerer tube, suggesting that the 5mm spacer should not be needed. And the Moots fork seems quite sturdy. But I want to hear it from Moots.
My question to Moots:
Is it OK to clamp the Moots fork at the very end without the 5mm spacer?
There seems to be some controversy about this... PAB refuses to do it without the 5mm spacer in place below the stem cap.
This is the response from Jon C at Moots, which settles the matter for me:
PAB is correct and they should follow the 5mm spacer above the stem instructions.
Keeps the end of the steerer from being crushed by the stem binder.
However, I’ve since had a conversation with Michael at Moots; there are some subtleties: cut just so, just the right length, it should be OK to go without the spacer. But he clearly recommends using the space, because cut a little 'off', and the pressure could cause excess pressure on the steerer tube if the spacer is not used. At least this is my take-away.