Hydroplaning Speed Calculator (Aquaplaning Speed from Tyre Pressure)
Rough speed at which tyres can start to ride up on standing water, from the tyre pressure, with the margin to the speed you drive at.
Results
The dashed line marks the value you entered.
What this tool does
The classic rule comes from NASA tests on aircraft tyres: the speed at which a tyre lifts off the road on a film of water is about 9 times the square root of the tyre pressure in psi, in knots. A car tyre at 2.3 bar (33 psi) gives roughly 90–100 km/h. It is a threshold for a smooth tyre on deep, standing water, not a promise: worn tread, a wide tyre, deeper water or a smooth surface all lower the real figure, so treat it as the speed above which the risk grows quickly, not as a safe limit below it.
Formula
V (knots) ≈ 9 × √(tyre pressure in psi) (Horne's formula) · V (mph) ≈ 10.35 × √psi
Variables
| Symbol | Meaning | Unit |
|---|---|---|
p | Tyre pressure | bar |
v | Speed you are driving at | km/h |
VP | Hydroplaning speed (approximate) | km/h |
VM | The same in mph | mph |
VK | The same in knots | kn |
MG | Margin below the hydroplaning speed (negative = above it) | km/h |
PN | Tyre pressure that would raise the limit to your speed | bar |
Worked example
- Tyre pressure2.3 bar
- Speed you are driving at90 km/h
- Hydroplaning speed (approximate)96 km/h
- The same in mph60 mph
- The same in knots52 kn
- Margin below the hydroplaning speed (negative = above it)6 km/h
- Tyre pressure that would raise the limit to your speed2.01 bar
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.