Based on that the 'hydroplaning speed' of a tire inflated to 45 psi is 60 mph. Besides other little instances, I lost it in turn 1 at MidOhio at 45 mph. Its on video tape.
Methinks the hydro speed is more a function of tread depth, rubber compound and tread design, and tire patch relative to weight than on the square root of the tire pressure times 9.
Where did that equation come from?