# set back seat post?



## Wayne (Sep 24, 2004)

OK, I am dumb. Why would somebody buy a setback seat post vs. a straight one? You can slide the saddle back on the rails and wouldn't that accomplish the same thing?


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## veloyellow (Aug 23, 2009)

Thomson claim that their setback seatpost is stronger. Other than that, there's no tech reason to use one. If you look at most non-Thomson straight seatposts, the rail clamps are setback in their mounting interface w/the post - the clamp position is the same as w/a setback post.
I needed a longer seatpost, so I bought a Thomson setback because I like the look, and they _do_ have a reputation for durability. 8K miles later, I still like it, but it was really just a personal choice that I could afford. YMMV


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## HarryCallahan (Nov 2, 2004)

There are several reasons, all related to fitting the "cockpit"

You can slide a seat back on the rails to a point. Slide it beyond the design limit and you risk bending the rails.

Or say you have a long torso relative to your overall height, or you want a more stretched out position on the bike or just need to sit further back, the set back post helps with this.


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## veloyellow (Aug 23, 2009)

Or say you have a long torso relative to your overall height, or you want a more stretched out position on the bike or just need to sit further back, the set back post helps with this.

This is a common misconception.

Hold a Thomson set-back seat post beside a non-Thomson straight post and you'll see that the rail clamps are in the _same position_ relative to where the seat tube of the bike is, in most cases. This is because Thomson mills the lower half of the rail clamp mechanism from the same alloy billet as the post, so it is directly on top of the post. Other brands usually install (crimp, rivet, weld, etc.) a rail clamp mech into the post, and they _set back the clamps_. Thomson had to develop the set-back post to accommodate for this and provide the same fit as non-Thomson seatposts.

Thomson makes straight seatposts as well, and these can be useful if you need to get closer to the handlebars, but this is not relevent to the OP.


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## dan0 (Oct 12, 2005)

veloyellow said:


> Or say you have a long torso relative to your overall height, or you want a more stretched out position on the bike or just need to sit further back, the set back post helps with this.
> 
> This is a common misconception.
> 
> ...


did I miss something or was the Op asking about setback posts in general not just Thompson. I have a Ritchey set back post and everything HC said is true. A setback post will help you get the proper fit (over the crankset) and also keep the seat clamp in the middle of the rails rather than at either end which leads to bent or broken rails


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## HarryCallahan (Nov 2, 2004)

*Reading comprehension?*

Vellowyellow,

I don't have access to both setback and straight Thomson seatposts, so I can't do a comparison. I wasn't responding to you; I was responding to the original post.

I can't say whether you are right or wrong, but I can tell you that I've got a set back post on my bike, fitted at a shop that does bike fits, because the stock straight post had me too close to the bars. Seems to have worked, and the difference is measurable.


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## traffic002 (Dec 16, 2008)

Wayne said:


> OK, I am dumb. Why would somebody buy a setback seat post vs. a straight one? You can slide the saddle back on the rails and wouldn't that accomplish the same thing?


If you're like me, and caught between two sizes of frames (Sm & M) if I go with a small frame, typically the seatpost angle is too steep for me. Thus a zero offset seatpost will put my seat too far forward and cramping my cockpit. The saddle rail only has so much adjustment (typically about 2")

On my Redline Monocog, I ordered a 15" because of the 17" frame's 31" standover height (I have 30" inseam) But the seat tube angle was too steep for my saddle to BB dimensions.

My bike came with a setback seatpost (approx 20mm) but I need more like 40mm. So I had to swap out a saddle with longer rails (which are hard to find.)

So...I would have preferred to run a seatpost with 40mm and run a standard saddle (more choices.) But I got things to fit with a saddle (Topeak) that had a 3" rail.

For another data point. My Cannondale Rush is a Medium. But has a slacker seat tube. So my saddle is actually pushed forward on the rails to create the same dimension cockpit and saddle to BB dimensions.

It's all in the name of proper fit. Your saddle to BB measurements are crucial do avoid knee pains, etc.


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## JPark (Aug 12, 2009)

dan0 said:


> did I miss something or was the Op asking about setback posts in general not just Thompson. I have a Ritchey set back post and everything HC said is true. A setback post will help you get the proper fit (over the crankset) and also keep the seat clamp in the middle of the rails rather than at either end which leads to bent or broken rails


Maybe not a direct answer to OP, but very useful and pertinent information(if it is true).


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## bankofdad (Dec 19, 2006)

I had to put a setback seat post on my cannondale prophet to get my knee over the pedal axle but in doing so the front of the bike would come up faster and easier on climbs since it put my weight back to the rear of the bike,just something you might run into if you get a setback post.


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## Toge-one (Aug 25, 2008)

FYI - the rail clamps on a Thomson setback seat post are 16mm further back from their straight seat post. In my case, this allows me to have the saddle rails in the optimum position and not all the way back (beyond the 'max' line). This will hopefully prevent my saddle rails from bending or snapping.


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## dirtdan (Jun 27, 2011)

Sure, if you need to go farther back than the rails allow.


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## Michael_L (Jul 27, 2005)

I am 6'2" and with a straight seat post with the saddle set back all the way I was still too cramped. The setback seat post has solved the problem for me.


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