I work with a guy that claimed to have figured out his bikes 'harmonic'. Without saying that the insane vibration was not normal, he determined that it was worst between 40 mph and 60 mph. His solution was to rapidly accelerate up to 60 and just hold it there. When slowing down to avoid the shakes he would use his 'late braking technique'. Which any time that I rode with him, I observed this to be a dangerous practice. However he is still alive, the bike in question (HD ultra), not so much.

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter