We can give this to you piecemeal or you can get it from an authoritative source. https://www.parktool.com/en-us/blog/...gth-and-sizing

This recommendation is often missed: "Generally, manufacturers recommend no more than 20mm additional stack height between stem and upper race." Two cm from the top bearing sounds over-restrictive. Two cm from the top of the compression cone would be more like it. But confirm with the manufacturer of your fork.

the rule of thumb I heard before (no idea from where) was that for CF steerers, the spacer stack should be no higher than the diameter of the steerer - so ~25mm for a 1” steerer and ~30mm for a 1 1/8” steerer. Seems a reasonably conservative approach. FWIW I’ve always run 20mm of spacers with a 1 1/8” steerer.

Some also recommend that you leave some steerer above the stem, so that the stem isn't clamping on the unsupported cut end of the steerer. I don't like the "chimney look, so I cut the steerer a couple of mm below the top of the stem, so the top cap sits directly on the stem. However, I reinforced the steerer with epoxy, so the top couple of inches containing the expander and where the stem clamps is solid. I pushed a small styrofoam plug (maybe sponge? Can't remember) into the steerer to contain the epoxy, installed the expander, then screwed in a long greased bolt to keep the top cap bolt receptacle open. Added epoxy up to the top of the steerer and let it set up. I spent most of a year ensuring that the stem was right where I wanted it before I committed the steerer to its current length. It's no longer adjustable, but it's also no longer crushable.

40mm of spacer stack is the usual industry maximum for years and years when the steerer is carbon or aluminum - but read the fork manual.

Having the expander go past the bottom of the stem is a bad idea. You're creating a stress riser by putting the exander end where the steerer isn't supported on the outside. Snap!

40 cm is 16 ins.

Corrected to 1.6 ins.

If would have been fairer and more accurate to say corrected to 40mm.

Fairer? The two measurements differ by 0.64 mm or 25 thou, which is within tolerances when cutting a steerer tube.

Context---- follow the thread.

I meant fairer to you, in that you pointed out an error, and it was corrected in a way to make it seem that you were wrong.

No, it wasn't. No part of my post makes it look like anyone was in error but me. It was a joking response to correct 40cm to 40mm and then write 1.6" in reference to the mentioned 16".

That's exactly how I read it, it seems obvious but I guess others can see it differently.