Aquaplaning
The formula I used for many years to calculate aquaplaning speed on a contaminated runway was one I got from an old flight safety film that showed US aircraft landing under various adverse circumstances.
The research concluded aquaplaning would start above the speed given by:
8.6 x sqrt tyre pressure in psi
So 2 questions:
1. Is there a better, proven modern calculating method?
2. Does it apply to any tyre (for e.g. a car) or is it restricted to ac tyres through some limitation such as tread pattern?