The sports car Paul Walker died in was so gnarly to drive ... Porsche WARNED its dealers, in writing, about letting just anyone drive the vehicle ... because it's hyper sensitive to road conditions.
TMZ obtained a copy of a memo sent from Porsche HQ to multiple dealers in the Midwest back in 2004 ... right before the $500K Carrera GT went on sale -- and it explains how ridiculously powerful the car is, but also that ... "this vehicle cannot drive over a Foster Beer can that is lying on its side."
In the doc, a Porsche exec says, "You need to be aware of what type of road surface you are on (dips; pot holes, seam heights, etc.)"
It's worth noting ... the road where Paul and Roger Rodas crashed is covered with reflective dots -- y'know, the ones you've probably driven over harmlessly thousands of times. Of course, you probably weren't driving the GT ... which some pro drivers have called "brutal and savage" and difficult to control.
Police are still investigating the exact cause of the accident, and, so far, have only said speed was a factor.
The exec's memo explains the GT is damn close to being a real deal racecar, but adds ... "This car has all the disadvantages of a racecar."
While Rodas was known to be an experienced driver -- the Porsche document makes it clear experience isn't always enough ... if the road surface isn't ideal.