Originally Posted by RatherPlayThanWork
I always thought it was the 2nd buckle that was to kept tight, as it keeps the heel down in place. I tend to not like the upper buckle super tight, just tight enough to keep the Booster in place under the shell.
For best performance, you want the top buckle tightest, with the second buckle looser (but not sloppy or undone). If you tighten the second buckle, and leave the top buckle looser, this will work not too badly in good conditions, but at higher speeds, on harder surfaces or in heavy crud, you'll lose some of the control and responsiveness that you would like to have. If you tighten both buckles, you'll have quick lateral movement transfer, but you'll lose some ankle mobility.
Just to clarify, when I say "tight" I mean holding things firmly in place, but not uncomfortably tight. How tight does vary with conditions & weather: for example, I go another buckle notch tighter if it's a warm day.
If you feel you need the second buckle tight to keep your heel snug in the heel pocket, I would wonder if your fit might be a bit too generous. The bottom two buckles on the lower shell section should hold the foot reasonably well in place, even with the upper cuff buckles loose or undone.