Seat Post setback

[oldforester]

What are the benefits of a seat post set back other than increasing the length of the top tube? TIA.

[Fixed]

the kops told me to
cheers

[LouDeeter]

Setback, whether from the seatpost or the seat tube angle, should be used to get the proper position over the bottom bracket and crankset in my opinion, not just to lengthen the toptube. I break the length of the toptube into two sections--the section behind the bb (setback) and the section in front of the bb. The seatpost and saddle rails are used to adjust the setback portion to attain fit. The stem is used to adjust the forward section for the same reason, after the rider position over the bb is set. The play on words of "the Kops told me to" is in the right direction.

[Fixed]

cheers

[roguedog]

Further, typically it seems frame builders seem to assume the rider will use a seat post with setback when they design frames. I may be wrong since this info is gleaned from following online discussions.

However, if correct then that means they've assumed where a rider's position is when designing the frame. Seems like one shouldn't alter that unless fit issues (e.g. back, flexibility, etc) dictate.

Experts and more knowledgeable folks correct and educate if I misstate here. (Long way to say I agree w/ fixed and lou. :-) )

[Ti Designs]

Until you get the saddle to pedal relationship right, you need to forget about where the handlebars are, so top tube lenght at this stage is a non-issue.

Think about sitting at a desk. You sit on a chair, you lean forward to work. As your center of gravity shifts forward of your hips the weight transfer is to your feet. If you move your feet back a bit (reducing the setback) at some point your center of gravity is going to be ahead of your feet and your quads will engage to keep you from going face first into your desk. My point here is that setback, be it from seat tube angle or seatpost setback, is to allow the rider to transfer their body weight to their pedals.

[LouDeeter]

[QUOTE=roguedog;1110010]Further, typically it seems frame builders seem to assume the rider will use a seat post with setback when they design frames. I may be wrong since this info is gleaned from following online discussions. "

I believe you are correct, although a lot of framebuilders will discuss the type of seatpost you use. A Boston area framebuilder who has authored many articles on fit had a discussion with me a few years ago. He had not kept up with seatpost designs and didn't know that many people were using non-setback seatposts until I pointed it out to him. He had based all his computations on a typical Campagnolo seatpost setback distance.

[Ken Robb]

the kops told me to
cheers

groan!:)

[giverdada]

when carl strong built my frame, he suggested that i use a non-setback seat post, and designed the frame accordingly. it's been beautiful.

that said, sometimes a saddle rail issue, or its interface with the seat post, or whatever, will influence the positioning of the saddle, and thereby the rider, over the BB. my brooks B17 required as much setback as possible because of the shortness of the rails, and where they interfaced with the seat post, relative to where i sat in the saddle.

and i really appreciate TiDesigns' explanations. just thinking about my position in his terms has favourably changed my riding. thanks for those, Ti.

[aaronv]

Seconding on the issue with the B17. I setup a new bike with a zero setback (new to me) with the B17 (known to me) and the fit was close but not right. With the zero setback had I to put the saddle at the end of the rails which is not the best. Replacing the post with setback provided enough adjustment range. Those rails are short!