What is the cause of a flat spot while driving

Hi Khalil:
There are two sources that I am aware of:

1) If an emergency stop was made and the tires wire locked up, as the vehicle skidded to a stop, rubber was scrubbed off the tires from friction with the pavement. When trying to drive on these tires, the flat spot will cause a discernable "bump" when impacting the pavement.

2) While not as common, older or inadequately inflated tires on parked vehicles will present a "flat spot" when the vehicle is first used. This will be particularly obvious in cold weather. As the tires warm up while being used, this flat spot circumstance typically cures itself.

Hope this helps.