Hi I want to get a new seatpost. I know the measurements of my seatpost- 27.2mm X 250mm. However, I am not entirely sure if this is a setback seatpost or not? Please see the attached picture and comment.
Thanks.
David

Yes, it's a setback post. Setback describes a seatpost whose saddle clamp is behind the centerline of the post. This was standard for years, but nowadays many posts have clamps directly in line with the center of the post like this Thomson post.

You determine the amount of setback by measuring horizontally from the centerline of the post to the center of the saddle cradle. Yours appears to be about an inch or so.

You will note the clamp that grips the saddle rails
is behind the center-line running thru the seatpost.

Then you can measure and determine amount of setback,
some offer more some less.

some saddles will let you shift the saddle back more to adjust setback ..

Thanks Everyone.

The Thomson seatpost FBinNY reference was designed with no setback to allow the post and the bottom of the saddle clamp to be made all in one piece for strength. Apparently Mr. Thomson had a two-piece seatpost break while he was riding and was determined to make one that would never happen to.

Thomson makes a "setback" seatpost by bending the cylindrical portion of the post backward slightly. The "kink" is about 3" below the saddle clamp which limits how far you can lower seatpost into the frame.

Here's a pic of a Thomson setback on my mountain bike. I've always had good luck with Thomsons on my mountain bikes, and I needed some setback to get the right fit on this particular bike, so I went with the Thomson setback. Although it looks kind of dramatic with the bent shape, it actually has about the least amount of setback of any setback seatpost you'll find, just 16mm. Most setback seatposts have 20-25mm of setback, and of course most of them get their setback from their shape at the top, not well down the post like the Thomson.

I have a Thomson set-back on one road bike and the bend starts about 2 cm above the seatpost clamp so there isn't a lot of downward adjustment available. I also need a set back post and the Thomson is adequate. Also, at the time I bought it there weren't many 31.6 mm posts available and I didn't want carbon. It's been very good and I'd get another in a minute.