Originally Posted by
DaveSSS
That is the standard measure - center of post to center of clamp, but the real measure of maximum setback potential on a post is determined by the distance from the front of the clamp to the centerline of the post. The clamp length might be 3cm on one model and 4cm on another. The one with the shorter clamp could have the same setback value, but actually allow another 5mm of rearward movment. None of the Thomson models has as much setback as most traditional post.
One of the oldest standards places the front of the clamp close the seatpost centerline, so a 4cm long clamp would have 20mm of setback. My FSA posts have 5-12mm more setback than that.
Thanks for the info. I attached a photo of the bike with the post I'll be swapping out. I believe c-c is about 20mm. The Thomson setback is 16mm. Would you say these posts have comparible setback? I'm hoping that if I go to the Thomson setback I'll be able to dial in the saddle so my reach is the same, and the saddle sits nicely between the limit marks.
Good thing is that I should be able to sort this out at the LBS before getting the new post, but thought I would ask here to get an early indication if this is possible.