Generic Vibration question

Not sure I can help or not but,

What is "normal" ?

You'll have to pardon my ignorance, but a little clearer explanation of "range of frequencies" may help.

I would contact ride control companies such as moog, monroe, gabriel perhaps?

Google "Reed Tachometer" It is a device that records frequencies in vehicles to help determine noises that cant be found otherwise. Saw it in use at GM training center, pretty neat but not real affordable for the average shop

I am trying to theorize a piezoelectric sensor which will respond to the vibrations of the car bumper. To design one such sensor I would like to know if anyone has measured low audible frequencies that we sometimes hear due to the road conditions otherwise due to the general engine vibrations. The piezoelectric sensor I am designing will respond to such vibrations and send a charge signal which will be later converted to some kind of useful voltage.

Please let me know if I am still not clear. Thanks for replying

I was interested in the natural frequency of vibration of the car in general.

What kind of question is this?

Student research enlightenment question.