So my car starts shaking, usually around 80 mph, sometimes just over 70. On the highway, smooth asphalt. Any ideas why? Simple balancing issue, or more?

 

Do you feel it in the steering wheel?

 

Only slightly. Most of the vibration comes from the pedal and the car in general. This is different than in my old Toyota, in which the steering wheel would shake side to side, but nothing else (that was always corrected by a tire balancing).

 

look for a balancing issue in the back or maybe a bent wheel. then look for cv/u joint problems.

 

It could also be caused by a tire out of round, especially if old.