Integrated seatpost, integrated seat mast, ISP…in the past few years there have been a number of different frame designs on the market that eschew a traditional, round/cylindrical seatpost that inserts into a seat tube. Instead, these frame designs have seat tube structures that extend far beyond the top of the top tube and incorporate some sort of specific fitting to hold the saddle atop. What does an ISP offer? Is it the wave of the future? What should you know before you buy one?
ISP: marketing, weight, structural, practical
First of all, “ISP” appears to be a Giant Bicycles product name, but since it’s convenient I’m going to appropriate the term for this article. I’m going to refer to the piece that attaches the saddle to the “integrated seat tube” (or “seat mast”) as a seatmast topper, which is actually Ritchey Design’s term for their product that several bicycle manufacturers, Scott among them, use for their own ISP frames. In addition to fore-aft/tilt of the seat clamp like conventional seatpost, a seatmast topper frequently allows for some measure of vertical seat adjustment on the ISP, which must otherwise be trimmed to a specific height. Since the seatmast must be cut, typically by hacksaw with a guide, fitting the ISP bike to a specific rider means permanently modifying the bike, much like cutting down a threadless steerer will limit stem/handlebar vertical adjustment. To an extent, this issue is over emphasized by ISP critics; most mast toppers still allow 20mm of vertical adjustment. In fact, Ritchey and Giant offer alternate tall toppers that give an additional 50mm (+20mm adjustment), so it’s not like no one could ever make use of your ISP bike after you.