Cracked flexplate question

First, you need to verify what kind of vibration it is. Is it tire/wheel vibration or is it engine/drive train vibration?

Very easy to differentiate. If you can feel the vibration as a low frequency vibration (vibrations far apart) then it is likely tire and wheel related.

If the vibration is high frequency (vibrations close together) for instance like a heard of pissed off bumble bees, then you have an engine/drive train vibration.

Also, does it vibrate with the engine running and the car sitting still? Run it up in RPM in park and neutral to the RPM where you feel it driving and see. This will tell you if it is between the balancer and torque converter.

If there is no vibration with the engine running and the car static, then you have eliminated the engine and torque converter.

Try all that and report back.