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Setback seatpost - why not smaller seat tube angle?

Started by Konstantin Shemyak · · Last activity · 7 posts · 597 views

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01 / Original postSetback seatpost - why not smaller seat tube angle?Konstantin Shemyak · 7 Apr 2006 02 / This pagePosts 1–7Page 1 of 1 · chronological order 03 / Latest replyPost #7Jasper Janssen · 9 Apr 2006

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Original section
Cycling Equipment
Published
7 April 2006
Last activity
9 April 2006
Original author
Konstantin Shemyak
Posts
7
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Public discussion
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597
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Topics
Frame geometry

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  1. Original post
    Konstantin Shemyak
    Archived post
    #1

    Why most seatposts are made with some setback?

    Clearly the same rider's position could be achieved with slightly
    less steep seat tube and no-setback seatpost. Looks like "straight"
    posts are marginally lighter/stiffer, naturally because there is
    no extra material and because there is less leverage applied when the
    rider is positioned closer from the post axle.

    I guess that in days of old when there were only plane pipe seatposts
    the setback was there because there was no other seat clamping
    mechanism (or was it?); but now is it dictated by anything else
    than traditions in frame geometry, with steeper than needed seat tube?

    Thanks!

    Konstantin.

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  2. Art Harris
    Archived post
    #2
    Konstantin Shemyak said:

    Why most seatposts are made with some setback?

    Quoted message said:

    Clearly the same rider's position could be achieved with slightly
    less steep seat tube and no-setback seatpost.

    For one thing, most modern bikes have very tight clearance. Making the
    seat tube angle slacker would require longer chainstays to keep the
    rear tire from rubbing against the seat tube. That might not be a bad
    thing, but it goes against modern fashion.

    Secondly, since most seat posts have setback, frame makers assume that
    when designing their frames. Which came first, the chicken or the egg?
    I don't know, but as long as I can remember, most quality seat posts
    have had some setback.

    Art Harris

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  3. Email address hidden
    Archived post
    #3
    Art Harris said:


    Secondly, since most seat posts have setback, frame makers assume that
    when designing their frames. Which came first, the chicken or the egg?
    I don't know, but as long as I can remember, most quality seat posts
    have had some setback.

    Indeed - "in-line" micro-adjust seatpins seem a fairly modern
    phenomenon popularised by MTBs.

    David Belcher

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  4. John Forrest Tomlinson
    Archived post
    #4
    Art Harris said:
    Konstantin Shemyak said:

    Why most seatposts are made with some setback?

    Quoted message said:

    Clearly the same rider's position could be achieved with slightly
    less steep seat tube and no-setback seatpost.

    For one thing, most modern bikes have very tight clearance. Making the
    seat tube angle slacker would require longer chainstays to keep the
    rear tire from rubbing against the seat tube. That might not be a bad
    thing, but it goes against modern fashion.

    Secondly, since most seat posts have setback, frame makers assume that
    when designing their frames. Which came first, the chicken or the egg?
    I don't know, but as long as I can remember, most quality seat posts
    have had some setback.

    I've never used a seatpost with a zero-offset clamp, but perhaps one
    reason seatposts have some offset is that, at least with single-bolt
    clamps, it's very easy to ge to the bolt?

    JT

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  5. Michael Press
    Archived post
    #5

    In article
    <[email hidden]>,

    Art Harris said:
    Konstantin Shemyak said:

    Why most seatposts are made with some setback?

    Quoted message said:

    Clearly the same rider's position could be achieved with slightly
    less steep seat tube and no-setback seatpost.

    For one thing, most modern bikes have very tight clearance. Making the
    seat tube angle slacker would require longer chainstays to keep the
    rear tire from rubbing against the seat tube. That might not be a bad
    thing, but it goes against modern fashion.

    Secondly, since most seat posts have setback, frame makers assume that
    when designing their frames. Which came first, the chicken or the egg?
    I don't know, but as long as I can remember, most quality seat posts
    have had some setback.

    What is set-back, and what is not set-back? I understand
    the classic seat post to have the front of the hold-down
    clamp centered on the seat post tube itself.

    --
    Michael Press

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  6. Art Harris
    Archived post
    #6
    Michael Press said:

    What is set-back, and what is not set-back?

    Quoted message said:

    I understand
    the classic seat post to have the front of the hold-down
    clamp centered on the seat post tube itself.

    Most classic road seat posts have the clamp set back from the
    centerline of the post.

    No set-back:
    http://www.lhthomson.com/images/sp_elite.jpg

    Set-back:
    http://i8.ebayimg.com/03/i/06/b5/fe/13_1.JPG

    Art Harris

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  7. Jasper Janssen
    Archived post
    #7
    Art Harris said:

    Secondly, since most seat posts have setback, frame makers assume that
    when designing their frames. Which came first, the chicken or the egg?
    I don't know, but as long as I can remember, most quality seat posts
    have had some setback.

    Back before micro-adjust, when seatposts were plain pipes and saddles had
    separate clamps, the relationship those clamps made between the top of the
    seatpost and where it clamped the saddle rails involved a bit of setback
    or setforward (if you wished, few people did), due to the natural geometry
    of the clamp.

    That's why modern seatposts have setback, 'cause they had to deal with
    frames that already assumed that geometry.

    That old clamp type was, as far as I know, already ubiquitous and standard
    before WWII.

    Jasper

    Report

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