fork tuning,, one of the problems often encountered with forks is too much rebound damping ,
on your static test the forks feel fine but over a set of roots the forks will eventualy run out of travel
the rebound is too slow the fork fails to return to it's full height before hitting the next root and this continues until you run out of travel or roots,,
to test for this you need a set of nasty roots,, or lay a long ladder down on the ground and ride along at a reasonable speed and using your cable tie check out your max travel or if you are a techno geek like I used to be just use your data logger
try varing speed to see if it makes it worse or better
you can use the same method to set up the rear of a full suspension bike ,
one other thing i know it seems a bit anal but keep a note book for your bikes and note any changes made and effect then you can go back to a setting that worked over a course ,,, the biggest problem i found in setting peoples bikes is they had no idea what changes they had made,,, since they last raced at a particular course which meant starting to set up from scratch
i could go on but i wont bore you with any more
Adrian Ward