balance the tires
You have a tire or tires out of balance.best to get tires road force balanced.
two possibilities: loose motor mounts or contaminated gasoline. In addition, if you are saying it shakes going down the road at around 55 mph then you may have a tire out of balance, or a bent wheel.
55 mph (!)
If the rotors are warped it can cause a shake when you hit the brakes.
Need more info. Does just the engine run rough or does the steering shake or does the whole vehicle shake betwen 50 and 55 mph?
A car going 55 mph is traveling at about 80.667 feet per second.
Yes, but any faster and you'll eventually hit the car in front of you?
Sure. If there are mud and rocks in the rim, the SUV can shake at speeds lower than 55 mph. Check the rim to see if there's anything in there that shouldn't be there.
Most common reason is improperly balanced wheels, next would be alignment but that usually causes a pull to the left or right.
55 mph. If the car stops (impact) people inside are still moving at 55 mph. They will hit the inside of the car- at 55 mph. That has the same effect as if you were standing still, and were hit by a car moving 55 mph. Messy. Wear your seatbelt.
Stopping Distance = about 206.25 feet at 55 mph