Where to cut steerer?

[PoorCyclist]

I have 2.5 cm sticking on top of the stem and want to do the cut now.
I am not sure if I should cut it lower then the stem top, or just about flush and use 5mm spacer above.

The steerer expander plug does have a small lip on top, which needs to be accounted for? (1mm?) So the actual steerer would need to be cut even lower. I want to keep using that expander because it reinforces really well.

Manufacturer BMC seems to recommend 5mm spacer above, I have seen almost none in the peleton have that
the stem is sitting directly on the headset..

[Geoff]

That depends upon what expander and topcap set-up you are using. Generally speaking, you need to allow for enough room for the expander and top cap under the stem, which is generally a couple or three millimeters, no more.

When you cut the steerer, make sure you use a wrap of electrical tape to prevent the fibers from fraying. Use the finest saw you can find and cut only halfway through, finishing the cut on thhe other side. Clean-up your cut by gently beveling the outside edge with a fine file.

[socratease]

Cutting the steerer above the stem does a better job of distributing the clamping load of the stem upon the steertube. If you don't believe me, take a look at bikes that have both types of cut executed. Those with shorter steertubes tend to have more pinching at the top bolt of the stem versus the bottom. I imagine stiffness is likely increased by having a spacer above.

Would recommend a spacer above. If you can't stand the aesthetic of that, you can always chop it further.

[sungod]

i cut mine level with the top of the stem, stem-steerer is safety critical, i'd rather play safe

even with the lip on the plug, a 3mm spacer is plenty to allow the underside of the top cap to clear the end of the plug

if you use a top cap with a flat underside (or do some creative work on the cap with a dremel) you may be able to get away with no spacer, once you've clamped the stem the top cap is just a decorative dust cover

[Devon]

Agreed with above. Level with the top of the stem, with a 5mm spacer on top.

[showdown]

Our team bikes come from Colnago (Colnago America is located in Chicago where we are) and when picking up our bikes we were told under no circumstances should the steerer be cut level with the stem as this causes too much stress on the steerer. We were told to leave between 3-5mm (enough for one spacer) above the stem. Surely there are multiple opinions but I'll trust my bike manufacturer.

-J

[DaveS]

Cutting a steering tube flush with the top of the stem makes no sense. Either leave a little protruding above the stem, so it properly locates the spacer on top, or cut it slightly below the stem and use no spacer.

While cutting the steerer 2-3mm above the stem and using a spacer is wise for the mechanically inept, it's not necessary for anyone with a little skill. Tighten the top bolt with less tension than the lower and there should never be a problem. I've never cut a steerer above the stem and never had any problem.

[stella-azzurra]

I agree with DaveS here a 1/16" or 1/8" below the top of the stem is fine if you want to have the top cap flush with the top of the stem. The bolt that clamps the stem to the steer tube is well below the top of the steer tube at that point.