Owned a Litespeed ExtraLight. Got severe harmonic vibration at 38 mph descending down a smoothly paved/curvy canyon road in Utah.
Bike was slaloming from left to right and crossing the double yellow line. Attempted the usual clamping knees to top tube. No luck. Tried the alternative method of lifting butt off saddle. No luck. All this within seconds of the harmonics.
Made split second decision I did not wish to be hood ornament on an upcoming vehicle. Touched the rear break and rolled over the bars. Shoulder (no my clavicle) busted in 2 places.
Got rid of that bike.
Just my experience.