Conventional wisdom is to line up the gaps, but I seem to remember in some installation instructions that Easton(?) recommended opposite orientation to reduce the "cutting" of the frame edge into the carbon tube. I guess with the gaps line up, the seatpost sees more concentration of stress in the back? Maybe placing the clamp with the slot toward the front puts less stress on the bolt since the bulk aluminum clamp - and not the bolt - is taking a majority of the stress as your ass loads the seat cyclically.... It may also prevent the bolt from backing out as well and creaking.
Some newer design seat clamps purposely bias the gap slightly shifted from the slot cut into the frame. See pic. The white arrow is lined up to the frame slot. The bolt is also threaded into a pivot to reduce bending stresses on the bolt as its being torqued down. Pretty clever design. Look at all that aluminum directly behind the frame slot where stress will be the highest.
Honestly, I dont think it matters too much. Since I run carbon all the time, Ive stuck with the recommendation I read on some installation instructions years ago. Its always fun to see some pimple faced 18 YO bike mechanic "dress me down" with my incorrectly installed seat post clamp.
Thinking about all the stresses iit seems that frame manufacturers would want to put the slot toward the front... Hmmm...
Last edited by tj90; 09-22-10 at 09:57 AM.