Dynamic Hydroplaning Speed Calculator
Estimate dynamic hydroplaning speed from tire pressure using the common aviation rule of thumb for training and planning.
36 PSI: the FAA estimate and rounded shortcut
At 36 PSI, √36 = 6 and the FAA dynamic estimate is 8.6 × 6 = 51.6 kt. Rounding the coefficient to 9 would instead give 54 kt.
Neither result establishes a safe wet-runway speed. Other hydroplaning mechanisms and reduced braking can occur below this dynamic estimate.
Formula and method
FAA dynamic hydroplaning speed estimate ≈ 8.6 × √main tire pressure in psi. The commonly rounded 9 × √psi rule is a different approximation; neither establishes a safe speed or stopping distance.
The FAA Airplane Flying Handbook gives the dynamic estimate as 8.6 × √(main-tire pressure in PSI). At 36 PSI, that is 51.6 knots. This estimate does not predict a safe speed or stopping distance; viscous hydroplaning can occur below it. See the FAA Airplane Flying Handbook, Chapter 9.