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Is it right to think that after the preload is set, and the stem bolts are tightened, the stem cap becomes redundant? Will the preload be held fixed by the stem? If so, does that mean the stem cap can be removed after preload is set?

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    Are you confident in your stem pinch bolts not moving ever? – Criggie Dec 14 '20 at 21:20
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    @Criggie: You’ll have much greater problems if the stem is loose enough that the stem cap is all that’s holding it on. – Michael Dec 17 '20 at 7:38
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    @Michael You are correct - a stem is very unlikely to go from Tight (rideable) to Slack (sliding off) in a short window. but there's a definite sliding scale of friction. I can imagine a stem that is tight enough for normal riding, but could shift on a pothole, or a panic braking, or a technical rock garden. And it is possible for bolts to back off their clamping force over time without noticing. That's why a good stem wiggle is part of the basic M check you do monthly. – Criggie Dec 17 '20 at 10:07
  • @Criggie Can the stem cap and bolt be refitted when the stem becomes loose? – John M. Dec 17 '20 at 11:14
  • @JohnM. yes, pre-supposing you're not injured by the stem moving independently from the front wheel and any resulting crash ! – Criggie Dec 17 '20 at 11:31
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Yes this is correct. Once the stem bolts are tight, they hold the system together. The top cap can be loosened without releasing the preload. You could try it out and you should find that the stem remains fixed and no play will develop.

You'll still need the top cap next time you want to preload the headset, so perhaps not redundant... maybe furloughed is a better word ;)

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  • > furloughed lol – John M. Dec 14 '20 at 17:59
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    Yeah, technically you can remove it without being in danger but you probably want leave it in to keep junk out of your head tube and to allow you to adjust the pre-load if it needs to be adjusted. – Kibbee Dec 14 '20 at 18:45
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As noted, the cap is theoretically not needed to hold the stem in place, but in the rare situation you need a stem adjustment on the road/trail you'd have a hard time of it. I've removed a spacer above the stem to be used on a different bike after tightening the stem bolts and never had a problem riding on singletrack. But I put the cap back on, for the reasons below...

Mud & water could certainly enter an uncapped steer tube, but the bigger consideration for me is that in a crash, an open tube like that will want to take "core samples" from anything soft and squishy (like you, compared to the tube material). Handlebar end caps are more of a concern here, but that is why NICA (the youth MTB league I coach with) requires the steer tube to be capped to ride or race with a team.

"Furloughed" is a great picture, but "re-purposed" as a dust & safety cap is how I'd put it.

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  • The top cap makes a great place to mount your gopro/action camera. Some people like their bike headunit therre rather than on an out-front mount. I have my old fashioned bike speedo there. – Criggie Dec 16 '20 at 23:57
  • In the case when stem adjustment is needed, the cap and bolt can be easily refitted, right? – John M. Dec 17 '20 at 9:37

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