posted Jun 1, 2011, 8:25 AM by Donald Vescio
updated Sep 12, 2011, 8:11 AM
In response to a common question:
"How do you know once you have the fore-aft [position for your saddle] adjusted correctly?"
This is a tricky question, as a lot depends on other factors in your fit, such as the length of your stem and aerobars and the amount of drop that they have below the level of your seat. Another variable to factor in is your seat tube angle and your frame's overall stack and reach. This can be complicated if you only rely on linear measures (i.e., 48cm from nose of saddle to center of steerer tube, etc.).
Think instead this way--there are general range of angles associated with your knees, hips, shoulders, and elbows that appear to work well for most riders. For short events and an aggressive TT position, consider a 90-95 deg hip angle when your pedals are at 3.00 and 9.00 (horizontal). By sliding your seat back or forward, while keeping your bar and stem the same, you'll decrease or increase your hip angle, accordinly. A hip angle of 100-115 deg will work for longer distance efforts, up to 120(ish, +/-) for those with problems of back flexibility.
If you go with a shorter stem or raise your aerobars, then you may want to slide your seat back to maintain an equivalent hip angle. In other words, what you really want to focus is how you rotate your entire body around your bottom bracket as a fixed point, which is important when setting up roughly equivalent positions on a road bike and a TT bike. For me, my road postion (as based on my knee and hip angles), for instance, really isn't different than that of my TT position, even though my knee is considerably in *front* of my BB when I time trial, while it's *behind* my BB on my road bike.