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I just bought a custom fixed gear frame that comes with a carbon fork with carbon steerer, off a guy who already cut the steerer lower than the stem so that the cap can sit flush on the stem. Normally I would put a 5mm spacer above the stem, because it seems like the general best practice.

However the fork was already cut so that with the expander in, after tightening the cap, the top of the expander plug would leave 2mm below the stem. I might be able to find a way to shave the top part of the headset a bit to save like 1mm, and since this frame hasn't been ridden, it should settle in just slightly deeper after a few rides.

Either way, should I be worried? or is this normal that it is not a problem?

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  • I think some do it that way. My bike came like that. I only moved one spacer above later. I had a suspicion that it slightly deformed the stem by getting the bolt and the nut at thhe top closer together than at the bottom. But maybe it was just my impression. See also youtu.be/E_W4p_YmycU?t=112
    – Vladimir F Героям слава
    Commented Jun 10, 2020 at 20:33
  • No, you should not be worried. Why would you put a spacer above the stem? In most cases, placing a spacer on top is what bike shops do to retain some degree of adjust-ability. Normal practice from people that know about building bikes is to top cap straight to the stem.
    – Lucero79
    Commented Jun 10, 2020 at 21:47
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    @Lucero79 Some manufacturer recommend putting a spacer above the stem on carbon steerer. Not just for adjustability. Obvs, that doesn't apply here.
    – abdnChap
    Commented Jun 10, 2020 at 22:39
  • Here was thinking the spacer above the stem was purely because people like me are scared of ruining new forks by cutting too short so leave a bit extra just in case... :)
    – mattnz
    Commented Jun 11, 2020 at 1:13
  • Ideally the plug should be just in that position with the steerer tube between the plug and the stem. The plug keeps the tube from being crushed by the stem.
    – Carel
    Commented Jun 11, 2020 at 18:23

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Should you be worried, I wouldn't be. The alloy expander will stop the carbon steerer from being crushed. Remember the max torque on the stem bolts will likely be less than 6nm. (Use appropriate retaining paste and don't over tighten it!)

As you mentioned, a lot of people (me included) will recommend a 5mm spacer on top of the stem, with the steerer a bit longer, to be extra safe.

But plenty of people refuse to have spacers above the stem for various reasons, mainly aesthetics, and they are fine, assuming the expander insider the steerer is of good quality.

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    +1. Some manufacturers also explicitly say not to have spacers above the stem because then the plug won't reinforce the stem properly. Cannondale is one such.
    – Nathan Knutson
    Commented Jun 10, 2020 at 21:26

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