I got 4 slightly used tires for my Tour. They all seem about even in wear.They are Goodyear Eagles. After I got them, I noticed that 3 of the tires say Eagle RS-A and 1 says Eagle LS.

Is there any difference in the RS-A and the LS?

I need to know because sometimes while driving I can feel the car vibrating. The car vibrates strongy while accelarting from a low speed to a high speed.

The tires are 225/50/R16 and I have stock suspension. I use to have 205/50Z/R16.

The LS is a much less sporty tire. They're quite different. What is the vibration like? Does it only occur under acceleration, or does it happen when at a steady speed, coasting, or braking?

The vibration occurs during accelaration and steady speeds. The steering wheel shakes a little too.

Sounds like they are out of balance. Where did you get them mounted and balanced?

Another possibility is that they are worn from a toe problem on the last car, and out of round. However, that should be visible.

Its definately the balance (and possibly the alignment) of the tires. Same thing happend to me when I first got my Contour. At about 65 mph, the car would shake. After the balance, smooth up to 100+ mph... oops... I didn't type that... it was for research.