Keep in mind that youâ€™re asking for things that are mutually contradictory. For compliance, you want a skinny seatpost. (Because seatposts are cantilevered beams, bending stiffness for round posts is proportional to the fourth power of the diameter. In other words, diameter is easily the biggest single contributor to stiffness/compliance).TimF wrote: â†‘Thu Mar 14, 2019 12:06 amI have a Canyon VCLS S15 on one of my bikes, which I find really comfortable and not too bad for weight. I could potentially pick up another one and shim this to 31.6 as they only come in 27.2 however I'm wondering (as I'm not sure how good that'll look) what else is comfortable and light?
Thatâ€™s why these flexy seatposts are always offered in 27.2mm diameters, and why (IMHO) some new Cannondales come with 25.0mm seatposts. The smaller the diameter, the better these compliant seatposts work.
Because of that fourth-power relationship between diameter and stiffness, a 4.4mm (13%) decrease in diameter (from 31.6mm to 27.2mm) results in a relatively huge increase in compliance. Under the same conditions (seatpost extension, material, wall thickness and loading), a 27.2mm post will flex (displace) about 58% more than a 31.6mm post.
One way to think of this is that for a given seatpost weight, a smaller-diameter seatpost will flex more than a larger-diameter one. You asked for the most comfortable light post, so it sounds like you want the most flex per mass, right? If so, go for a shimmed 25.0mm or 27.2mm post. But some people wonâ€™t like the idea of a shimmed post, which I understand. If youâ€™re among them, youâ€™re looking at a stiffer 31.6mm post.
I hope that helps!