Its not just the height of the seat, fore/aft of foot position. Its a lot of little things like position of the seat in relation to the bottom bracket. Seat forward for those tri-athletes and some TTs. touring seat is placed further back. the length of crank 165mm, 170mm 172.5mm and 175mm. The height of the handle bar in relation to the seat height, Stem length. Width of the handlebar too.

I'm still fiddling with my seat height and looking for a 165mm cranks. Standard 172.5mm is way way too big for me. It seems too many people overlook the size of the cranks. They worry about leg extensions, fore/aft of the knee, the position of your foot in the pedal, seat height, handle bar height, and sometimes the angle of the seat.

Getting a professional fit is a big big plus. I been hesitant to get fit professionally on my e-bay purchase of Obera bike. Handle bar too wide, cranks standard 172.5mm instead of 165mm (oops!) Do I want to spend more money for 165mm cranks? Not sure FSA carbon comes in 165mm (oops again). and new easton handle bar ($$ ouch). So I'm just making do. Few things learned about buying a bike on e-bay. good deal if you don't care too much about perfect fit.

Good fit, priceless. your body will thank you.

Shawn