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Why are top caps tapered?

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Why are top caps tapered?

Old 05-03-21, 09:58 AM
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Ti473
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Why are top caps tapered?

I was looking in my small parts bin and noticed that a lot of headset top caps have that conical shape on the bottom side.
I find it kind of annoying as you have to leave extra gap between the top of the steerer and the last spacer, otherwise the cap ends up bottoming out on the steerer plug and doesn't actually put any preload on the headset. Sometimes that gap is as much as 5 mm, so you have to use a 10mm spacer (unless you have a 7.5 laying around) as your last spacer.
Can't they just make them flat?
Rant over
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Old 05-03-21, 11:33 AM
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Originally Posted by Ti473 View Post
I was looking in my small parts bin and noticed that a lot of headset top caps have that conical shape on the bottom side.
I find it kind of annoying as you have to leave extra gap between the top of the steerer and the last spacer, otherwise the cap ends up bottoming out on the steerer plug and doesn't actually put any preload on the headset. Sometimes that gap is as much as 5 mm, so you have to use a 10mm spacer (unless you have a 7.5 laying around) as your last spacer.
Can't they just make them flat?
Rant over
Clearly, the top cap makers are in cahoots with the spacer manufacturers.
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Old 05-03-21, 09:31 PM
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Thruhiker 
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Wolftooth makes some pretty neat ones. You can even do away with the spacer.https://www.wolftoothcomponents.com/...ted-5mm-spacer
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Old 05-04-21, 06:26 AM
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Originally Posted by Ti473 View Post
I was looking in my small parts bin and noticed that a lot of headset top caps have that conical shape on the bottom side.
I find it kind of annoying as you have to leave extra gap between the top of the steerer and the last spacer, otherwise the cap ends up bottoming out on the steerer plug and doesn't actually put any preload on the headset. Sometimes that gap is as much as 5 mm, so you have to use a 10mm spacer (unless you have a 7.5 laying around) as your last spacer.
Can't they just make them flat?
Rant over
The taper on a stem cap shouldnít even come close to causing the top cap to hitting the steer tube. The edges of the cap might come in contact with the steer tube but the taper isnít the problem. The taper is actually a clever bit of engineering. It puts more meat at the center of the part so that the soft aluminum can stand up to the force put on it without having a bunch of extra metal you donít need.

As for spacers, they come in tons of different sizes and are relatively cheap. Just get some extra thin ones to have on hand.
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Old 05-04-21, 09:14 AM
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The taper was never a problem for metal steerer tubes with star nuts and actually made the cap stronger, while reducing weight. They do pose problem with trying to use them on a carbon steerer with a compression plug, which sits flush (or nearly flush) with the top of the steerer. Most compression plugs come with a top cap that doesn't have the taper and work fine with a 5mm spacer on top of the stem.
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