This is non related to a Ranger specifically, but i've always had good help here so I figured I'd ask anyway as it seems like it would be general vehicle knowledge as opposed to brand specific.

My car (06 Cobalt SS) vibrates very rough (like I'm way out of alignment or something) at about 80-100KMPH but at about 110 she's smooth.

Does anybody have any ideas off the top of their head that could be the cause? It seems to me that if it was bad at 80 it should be worse at 110. :s

 

It could be something as simple as a wheel out of balance or a bad tire. Try rotating them to see if the vibrations move with it.

 

x2

Tire could be out of round, Something in your suspension loose, do you have fix-a-flat or slime in a tire?

 

Not that I'm aware of - I just bought the car recently.