Which expression describes the hydroplaning speed for tires?

Which expression describes the hydroplaning speed for tires?

• A. Tire pressure divided by 8.6
• B. 8.6 times tire radius
• C. Tire pressure plus 8.6
• D. Square root of tire pressure times 8.6

Answer: (D)

Hydroplaning speed grows with the square root of tire pressure. In practice, a common rule of thumb is that the speed at which hydroplaning starts is proportional to sqrt(pressure in psi), often written as V ≈ constant × sqrt(PSI). The expression that follows this square-root relationship is the square root of tire pressure multiplied by about 8.6, which matches the typical constant used to estimate mph. The other forms—dividing by a number, adding a value, or involving tire radius—do not reflect how hydroplaning speed scales with pressure, so they don’t match the established relationship.

Hydroplaning speed grows with the square root of tire pressure. In practice, a common rule of thumb is that the speed at which hydroplaning starts is proportional to sqrt(pressure in psi), often written as V ≈ constant × sqrt(PSI). The expression that follows this square-root relationship is the square root of tire pressure multiplied by about 8.6, which matches the typical constant used to estimate mph. The other forms—dividing by a number, adding a value, or involving tire radius—do not reflect how hydroplaning speed scales with pressure, so they don’t match the established relationship.