I got my motobecane partially disassembled and I did all tuning and alignment myself. Being a new joiner it makes me feel I am missing some point. The issue is when my bike is on the stand the shifting is smooth for all 3x8 gears, but when I seat or especially drive with bouncing I cannot reach lowest 2 gears in the rear or they jump up and down. Adjusting b-screw seems helped a bit or this is just my impression. Shall I look into rear scock initial preload? Looks like my sag is too big?