As you might expect, the Cane Creek Thudbuster/ST far exceeded the flex, both horizontally and vertically, of any of the other seatposts. The model tested was the ST (short travel) version with 33mm of travel. Just by sitting on it, the saddle moved down over half an inch and back almost 0.8 inches. This probably explains the Thudbuster/ST’s widespread usage as a stoker seatpost on road tandems. While it offers little advantage over much lighter posts on high-frequency vibrations, it takes out the big bumps that the stoker cannot see.
Interestingly, the seatpost with the worst high-frequency vibration performance, the Ritchey WCS Carbon straight post, had the second-highest vertical flex reading, behind only the Thudbuster/ST. Apparently, since it let the saddle rails move so far, the rails were less inhibited from passing on the vibration to the rider. Strangely, its sister post, the Ritchey WCS Carbon with 25mm of setback, had the next highest flex — clearly due in large part to the seatpost and not just the seat rails, because the saddle was pushed most of the way forward. Even stranger, both Ritchey carbon posts exhibited more saddle flex than the Cannondale SAVE post with the flattened section specifically designed to flex.
Due to the fact that we measured flex at the tail of the saddle, the seatposts with the lowest flex numbers were all setback seatposts: the Thomson Masterpiece (16mm setback), the Zipp Service Course SL aluminum (20mm setback), and the Moots Cinch titanium (19mm setback). Breaking up the run of setback posts, the Moots Cinch titanium straight post just barely took the next spot ahead of the FSA K-Force Light SB25 carbon (25mm setback). The stiffest seatpost, and the only one to register under 0.15 inch flex in either direction (and it did it in both) was the Thomson Masterpiece setback, while the Zipp Service Course SL aluminum setback was the next stiffest and the only other one under 0.16 inch flex in either direction (and it did it in both).
How Seatpost Material Affects Saddle Flex
We tested only one model in both aluminum and carbon, the Ritchey WCS. Comparing the two — both with 25mm setback — we find that the flex of the carbon model is greater in both the horizontal and vertical directions than that of the aluminum one. Bottom Line: Carbon posts deflect more than similar aluminum posts, which is good for big hits.
Flex: Setback vs. Straight
In all cases except one, both the vertical and horizontal flex on the setback posts were less than on the straight posts of the same make and model. That one exception was the Ritchey WCS Carbon: The vertical flex with the straight WCS post was indeed greater than that of the setback version, but the horizontal flex of the straight WCS was slightly less than that of the setback WCS, breaking an otherwise straight flush of straight over setback. Perhaps that is due to the superlight Ritchey WCS Carbon setback post flexing just below the head, allowing it to move back 0.01 inch more under the rider’s weight. Bottom Line: If you’re concerned about maximizing seated pedaling efficiency, consider a setback post.
Flex: Seatposts with Suspension Features
As noted and expected, the flex of the Cane Creek Thudbuster/ST greatly exceeded that of all of the other seatposts. It is the only one in this test with pivots; it is designed to move a long way while others can only flex along their length. The movement of the Specialized post with the Zertz elastomer plug is quite modest; it finished in fifth in horizontal movement and seventh in vertical flex. The Cannondale Flash post finished sixth in horizontal and fourth in vertical flex. Both Ritchey carbon posts still had more flex than the Cannondale SAVE. Bottom Line: The Specialized and Cannondale seatposts excel at damping vibration, however, the designs do not compromise pedaling efficiency.
Ease of Saddle Installation and Adjustment
This was not intended to be a test of the ease of setup of the various seatposts, but given that we had to swap and quickly set up saddle positions on 14 seatposts many times over two days of testing, we learned some things about that as well. The Ritchey single-bolt design, once you figured out how to avoid dropping all of the little separate pieces, was by far the easiest and fastest to install and adjust. The other cross-bolt designs — the Moots and the Specialized — were also easy to install and, with more effort to overcome friction in the head, could be rotated to the proper position quickly. The two-bolt design of the rest of the posts, with one ahead and one behind the saddle clamp, allowed precise angular adjustment, but finalizing the riding position took longer. Finally, the pair of two-bolt posts (Cannondale and Cane Creek), in which one of the bolts was a thumb screw, were a significant pain to finalize the saddle tilt adjustment because the Allen socket bolt had to be loosened completely every time you wanted to turn the thumb screw.