Mitsubishi Repair: Shudder, worn shocks, car alignment

Question
I own a Mitsubishi Eclipse GTS, 2004.  I have noticed that when I hit the speed between 30-40MPH and hold it there. The car starts to shudder and shake.  If I let off the gas it stops as well as if I speed up.  I am perplexed and I am not sure where to start looking.  I have taken it in and had the tires rebalanced and a total car alignment and neither has helped.  Please advise Thanks, Jennifer

Answer
Jennifer,
There are a several reasons that cause this.  It's possible that you have a wheel (rim) that is warped.  When tires are balanced, a spin balance machine may only need to spin the wheel at about 15-20 mph to balance it.  If the rim is just slightly bent, it may not experience any wobble until 30-40 mph.  This can also be the case if your tires are over worn or unevenly worn.

Loose, worn or damaged wheel bearings as well as certain kinds of tread wear can also cause vibrations.  Problems with the vehicle suspension (worn shocks, struts, etc) can also cause speed-sensitive wobble and vibrations.  You can have your mechanic check your suspension components for problems.  And if you think you know a specific tire that may be causing the shudder, you can install your spare tire temporarily and drive with it.  This will let you know if the problem is specific to the tire/wheel or possibly suspension.
Good luck!