Mountain Biking - Why does Specialized used set-back seatposts?

I recently bought a frame on ebay, it is the same one you see here

http://www.specialized.com/bc/SBCBkModel.jsp?arc=2006&spid=21783

I am at the point of ordering a seatpost (thomson). I see that the bike is spec'd with a setback post, is this necessary because of the geometry or something, or would a straight post be ok on this frame? Thanks

It's just a fit thing. Setback seatpost just moves your weight backwards a bit. It's all a function of toptube length, seatpost geometry and stem length. From a technical point of view, sure you can run a straight post. From a fit point of view - that's a big "it depends".

A 'setback' thomson post is a bit misleading. Since the clamp design has zero offset to the post, a setback thomson post has about the same setback as most other brands 'regular' posts.

A regular thomson post (or any other zero offset clamp design) would theoretically put you forward about 20 mm.

But like GV27 said , its all about fit. Find the post position and height that gets you in the correct position as it relates to your pedals and go from there.

Plus don't forget the seat can be adjusted in either setup. So if you're running a setback post with the seat slid forward, you can go to a straight post no problem. And vice-versa.

Thomson found that by bending the post and using a zero offset seat clamp, it makes the overall package a little lighter than usinng a strait post and heavier offset clamp. My own measurements on my bikes show no difference in rider position.

My own measurements on my bikes show no difference in rider position.

OIC - that took me a minute to figure out. You mean no difference between the Thomson setback design and "conventional" setback designs, right? Thought for a second you meant straight fs. setback and i was like "Whatchu talkin' 'bout, Willis?".

I mean the strait post (specialized) with offset clamp that came on my Epic. Compared to the Thomson masterpiece setback post that I put on it. There is no difference in rider position. I did the upgrade for the weight savings and the somewhat neater look.

Thanks folks. I ordered the setback. The incredible details about cycling minutia avaliable in the collective brains of this membership always amaze me.