Do you ever notice a vibration (typically through the steering wheel or coming from the front of the car) after installing new tires or getting a tire rotation? A vibration at any speed indicates there's a problem. Naturally, it's something that needs to be addressed right away. A quick check of a few key areas will help determine what to do.
As soon as possible, use the vehicle's lug wrench to ensure all lug nuts are tight. The car manufacturer requires a specific torque (a unit of measure for how tightly the lug nuts are installed) for your vehicle, but a quick check to see if all lug nuts require the same amount of strength to tighten is a good first step. Mistakes are unavoidable, and if the installer didn't double check his/her work, this can be a quick fix. You can always go back to the installer once everything is tightened to have them triple check the torque.
The installer can get the vehicle back in the air and check for an improperly installed centering ring, missing balancing weight or other issues. If nothing seems amiss, the tires and wheels can be removed and put back on the balancing machine to check both of them for issues.
If the tires are worn and were recently rotated, one pair of tires may have had an existing problem that wasn't as noticeable with the tires in a different position on the car. Most garages will mention any wear issues like these to you before letting you leave, but a double check never hurts.
Finally, a quick check of your tire pressure may shed some light on the issue, so never rule anything out. Remember that any reputable shop will be happy to fix any problems that result from their work, so don't be afraid to give them a call with concerns.
To diagnose a vibration problem, view "Vibration Diagnosis Flow Chart."