What causes a shaky steering wheel at high speed?

Tire out of balance, bent wheel, defect in tire, loose wheel bearing, worn suspension parts are common causes. Have the tires removed inspected and balanced. Have all other parts inspected. Although the wheels being out of balance is usually the main cause, sometimes the rubber bushing located on the steering column, located about halfway down the Coulomb becomes worn, and causes some play. If problem still exists after wheel balancing, check condition of rubber bushing for looseness, or wear. Tom.