When I reach 45 MPH in my car it starts to vibrate. The tires are balanced and the alignment is good.
The speed you say the problem starts is just at the speed the transmission shifts into overdrive and locks up the transmission converter. The speed is also the time that most tire balance problems start to show up. Try to put your transmission in 3rd gear and get above 45 mph with out overreving the engine. This test should take the transmission converter issue out and if the vibration is still there then the problem may be a tire balance issue. I recommend you have a mechanic, like ones from YourMechanic, to inspect the car's vibrating issue.
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