Originally Posted by
e_guevara
Fit changes should be done gradually, allowing your body to get used to the new position.
A 10 mm difference IMO would not be much change. As the previous poster noted, 20 mm is enough to have a significant effect. I had the same problem (hand numbness, neck pain) on my race bike with the stock 100 mm stem. Swapping it out to a 120 mm made rides over 2 hrs better.
Dropping (slamming) the is good if you want to get into a more aero position.
I just had a fitting and went from a 100 to a 110mm stem due to hand numbness; it helped, but not significantly. Going to go back and ask for a 120mm stem.