Bam Margera -- That Truck Smashed My Porsche

Bam Margera's brand new Porsche was "smashed" ... in a traffic collision in Pennsylvania that happened just moments ago ... TMZ has learned.

The "Jackass" star tells us, "A big truck made a wide turn and smashed the whole left side. I just got the damn thing too."

Bam says he just purchased the car 4 months ago.

Witnesses at the scene tell us Bam appeared upset following the collision. We're told the driver's side mirror was hanging off the car and the driver's side of the car was all scratched up.

TMZ spoke with a member of the Pennsylvania State Police who told us the crash did not appear to be Bam's fault ... and no one appeared to be under the influence of any kind of substance.