My motorcycles get shimmy if I sit too far back on the seat and take weight off the pegs. Reweighting the pegs immediately straightens things out. My Centurion Pro-tour gets some shimmy with out tension on my front bag, strings to the handlebar or a decaleur stop it. If riding no hand I tend to put my weight on my seat, putting weight on the pedals stops the tendency to shimmy but that is hard riding no hands.