Originally Posted by
5teve
longer cranks will create a correspondingly shorter seatpost extension. For example, running 180mm cranks will allow you to lower your seat 5mm compared to 175mm cranks and obtain the same leg extension. 400mm is about as long a post as you are going to find so you may want to look for frames that feature an extended seat tube.
This is not necessarily true. Generally speaking, you may or may not have to adjust your saddle height with different length cranks.