Taller Stem Stack Height on Existing Fork?

[scoobydrew]

On one of my bikes, the steerer length is optimized such that I can place a 5mm thick spacer on top of the stem and a 10mm thick spacer on the bottom of the stem (between stem and headset). The current stem has a stack height of 41mm. The steerer is carbon for a 1-1/8" diameter headset. The compression plug has a 2mm lip.

If I want to swap out that stem for one with a 45mm stack height (+4mm), would there be any risks for that same spacer configuration (5mm/10mm)?

My understanding is that it should be fine as long as the upper clamping bolt of the stem is not above or in-line with the end of the steerer, so stem choice certainly plays into account. For instance a Moots stem has the clamping bolts towards the center of the stack whereas most stems are spaced further apart.

Thanks in advance

[skouri1]

So there are a few things to consider.
You can still put the 10mm spacer on the bottom. but you may not have anything to put the 5mm spacer on top then.
Most forks recommend a spacer above the stem so the stem does not crush the top of the steerer tube...

BUT
since you are moving from 41 to 45 stack height spacer, your new stem will have ~2mm more on both sides.
So to maintain your current bar height, you can actually swap the 10mm spacer for an 8mm spacer (zipp makes one, but there are surely others).
then you should probably be able to get the 5mm on top (but again depends how the steerer is cut).

[scoobydrew]

Thanks for the input. Good call on the 8mm spacer.