Setback seatpost - why not smaller seat tube angle?

[Konstantin Shemyak]

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.

 

[Art Harris]

Konstantin Shemyak wrote:

> 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.

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

 

[[email protected]]

Art Harris wrote:

>
> 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

 

[John Forrest Tomlinson]

On 7 Apr 2006 04:34:55 -0700, "Art Harris" <[email protected]> wrote:

>Konstantin Shemyak wrote:
>
>> 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.
>
>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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[Michael Press]

In article
<[email protected]>,
"Art Harris" <[email protected]> wrote:

> Konstantin Shemyak wrote:
>
> > 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.
>
> 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

 

[Art Harris]

Michael Press wrote:

> 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.

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

 

[Jasper Janssen]

On 7 Apr 2006 04:34:55 -0700, "Art Harris" <[email protected]> wrote:

>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