ultrazenith
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I have a sleeved seat post in an aluminium frame. If the bottom of the seat post is above the bottom the sleeve, where is the pivot point? At the bottom of the sleeve, or at the bottom of the seat post?
seat post shim / sleeve question - where is the pivot point?
- Thread starter ultrazenith
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kinda the bottom of the sleeve AND the bottom of the seatpost, but it's not even that straightforward...
Essentially, in a standard setup, it would be the bottom of the seatpost; Both for the seatpost and the frame.
In your setup, For the seatpost, it's the bottom of the seatpost, but for the frame, it's the bottom of the shim. ish. But what about the shim...?
...with a thin shim, that is split down one side for clamping, it gets really messy. The shim may splay out/deform where the seatpost ends, as it's neither an interference fit, nor clamped it's whole length. meaning that the point moves again to the end of the seatpost.
So, best assume it's the end of the seatpost TBH. Personally, I'd find a post that goes all the way through the shim.
Essentially, in a standard setup, it would be the bottom of the seatpost; Both for the seatpost and the frame.
In your setup, For the seatpost, it's the bottom of the seatpost, but for the frame, it's the bottom of the shim. ish. But what about the shim...?
...with a thin shim, that is split down one side for clamping, it gets really messy. The shim may splay out/deform where the seatpost ends, as it's neither an interference fit, nor clamped it's whole length. meaning that the point moves again to the end of the seatpost.
So, best assume it's the end of the seatpost TBH. Personally, I'd find a post that goes all the way through the shim.
old_coyote_pedaller
MacRetro Rider
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Re:
Depends what you mean by pivot point. If you load the seat-post in the normal manner, i.e. with yer bum on it, the saddle/seat-post combo will want to rock/bend backwards due to the angle of seat-tube. It will be restrained by the part of seat-post in frame/shim and will rotate or try to around where it is held in the seat-tube by the seat-post clamp. This clamp area becomes the pivot point as the post cannot move there but potentially can above and below clamp.
The shim isn't rigidly part of either the frame or seat-post so cannot transfer the load on the seat-tube from the bottom of seat-post much further down the seat-tube than where the bottom of seat-post is, it will only spread the load from the very end of seat-post so that it might not deform the front of seat-tube.
As mattr says if the the seat-post isn't all the way into shim, if it's a typical length shim, there's not enough seat-post in frame.
Depends what you mean by pivot point. If you load the seat-post in the normal manner, i.e. with yer bum on it, the saddle/seat-post combo will want to rock/bend backwards due to the angle of seat-tube. It will be restrained by the part of seat-post in frame/shim and will rotate or try to around where it is held in the seat-tube by the seat-post clamp. This clamp area becomes the pivot point as the post cannot move there but potentially can above and below clamp.
The shim isn't rigidly part of either the frame or seat-post so cannot transfer the load on the seat-tube from the bottom of seat-post much further down the seat-tube than where the bottom of seat-post is, it will only spread the load from the very end of seat-post so that it might not deform the front of seat-tube.
As mattr says if the the seat-post isn't all the way into shim, if it's a typical length shim, there's not enough seat-post in frame.
