I am kind of a big fella and when I bought my bike (61 cm) they put a MTB seatpost (330 mm) to make sure it was long enough. I have ridden this for four years with no problems, but I wanted to spring for a Carbon Fiber seatpost or lightweight aluminum to drop some weight. Problem is the longest road seatpost are 270mm.
Currently with 330 mm post, I have roughly 150 mm exposed and 175 mm inside the tube. If I went to a 270 mm post, I would only have 115 mm inside the tube. Is this enough? I am especially worried because a carbon post is more likely to snap off than a metal one.
If you only have 150mm exposed, a 270 would be plenty long. That being said, there are lots of extra long carbon road posts. I ride a TCR composite road bike, and have 230mm showing. I use a carbon Look Ergopost2 (which is 330mm long), but there are lots of other options. Compact geometry bikes are getting more and more common, and they require loooong posts.
On the fringes of this subject, am I just seeing things in thinking that some bikes’ geometry tends to end up with generally less post showing when correctly set up for a cross-section of riders? (obviously ignoring sloping compacts here)
In particular, looking at Cannondale’s road bikes (in publicity shots and in real life) to my eye they seem to generally show a little less post than, say, comparable Treks?
Or maybe it’s just a lifetime of me thinking that other people have bigger protrusions than I do…?
