If a car's steering wheel shakes when driving at high speeds, the cause is most likely a bent wheel. While that is the most common issue, such a problem can also be caused by suspension problems, according to O'Reilly Auto Parts.
A mechanic can diagnose a bent wheel by putting the car up on a rack and watching for wheels that don't spin evenly or that wobble while spinning. If this is the case, rebalancing or rotating the tires will often fix the problem.
While less likely than a bent wheel, damaged wheel bearings can also be to blame for a shaky steering wheel. Wheel bearings typically last for the life of the car, but it is possible for them to break and require replacement.
If there are no issue with the wheels or bearings, the problem may lie in the suspension. A car's suspension includes several components that are highly involved in steering. These components include shocks, struts, tie rods and steering dampers, which, if malfunctioning, can cause a steering wheel to shake at high speeds. O'Reilly Auto Parts advises that if the issue is suspension-based, the most likely cause is worn or loose steering dampers or tie rods.