On my 1998 Ford Taurus SE...?

[shadowwolf1262]

...It shakes on the highway at 70 MPH. Its not a very violent shake, more of a medium rumble. I just wanted to know if it could be caused my low tire pressure, I know my rear passenger tire is low, could that be the issue? Or could it be something more serious?

 

[Collin B (Elvis P)]

it could be tire pressure steering or your tire is not correctly on the rim

 

[I'd rather be outside]

If the shake goes away below and above 70 MPH, then one of the front wheels is out-of-balance.