tenet wrote:

I think it was 1952 the great London smog - as Jimbo says it was so thick you literally could only see a yard or two through the thick yellow mist. Breathing through a handkerchief rendered it black with soot. Thousands died of respiratory disease and it heralded the introduction of the clean air act.

Does that mean 9 times the square root is the speed?
In mph?
Therefore if it's speed and say 36 psi, so 6 times 9= 54 mph?

What depth of water?

Or is that on any water?

Does it matter on tread depth, tread pattern or tyre compound?

Does it matter wahat pressure the trailer tyres are?

Or just so long as they are harde then 36psi?

Hopefully these questions can be answered before it rains again.

Sidthecat wrote:

Sounds like a Monty Python sketch . . .

Well I remember once, they had to use a snow plough to clear the smog it was that thick

9 x sq root to the power of Z

Z being arbitrary. At work
At home

"I can't always believe facts I read on the web" - Charles Dickens

winner by default of the tractor vs caravan race

Dartman the one wrote:

With decent tread you will aquaplane at 9 x sq root of your tyre pressure. those towing heavy trailers or caravans will find that the the trailer or van won't aquaplane at legal limits due to much higher tyre pressures.

Mowog wrote:

Does that mean 9 times the square root is the speed?
In mph?
Therefore if it's speed and say 36 psi, so 6 times 9= 54 mph?

What depth of water?

Or is that on any water?

Does it matter on tread depth, tread pattern or tyre compound?

Does it matter wahat pressure the trailer tyres are?

Or just so long as they are harde then 36psi?

Hopefully these questions can be answered before it rains again.

Interesting.........thanks

Maybe its why road bicycles dont need tread - I wont aquaplane until Im doing 90mph !

But isnt it really due to the pressure exerted by the tyre onto the wet road -- wide tyre has a large contact area so pressure is low compared to a narrower tyre for same mass of vehicle.
Bicycle has tiny contact area so pressure is high despite low mass.

Pressure is force / area

Force is mass x acceleration, and is proportional to mass when gravity is the acceleration Jules

That looks more scientific

Jules, I initially thought as you, but then I realised that the surface area of the tyres in contact with the road was a direct function of the tyre pressure and the car weight.

As you lower the tyre pressure, more tyre area is needed to support the cars weight.

You were right to say that pressure is a measurement of force per area, so a freelander 2 weighing about 4000lbs (1000lb per wheel), with a tyre pressure of 35psi, will have a contact patch of 28 sq in per tyre, which on a 9 in wide tyre will be about 3 in long. It seems to work out ok.

Also, for any given pressure and weight, it doesn't matter whether the tyre is wide or narrow, large or small diameter, the contact area will be the same.

Although I imagine the water dispersant quality will vary with these factors as well as the tread pattern and depth. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

I think.....too many variables.............

The formula is from the aircraft industry, aircraft tyres only have longitudinal grooves continual around the circumference, side slots for squeegeeing water is an attempt to dry the road surface to improve grip they can't and won't stop aquaplaning. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

Aircraft tyres tend to run at much higher pressures.

An extreme example is the English Electric Lightning with a pressure of 350psi.

Therefore 19 x 9 = 171 mph theoretical aquaplane speed.

The long main gear legs retracted towards the wingtip, necessitating an exceptionally thin main tyre inflated to the high pressure of 330–350 psi (23–24 bar; 2,300–2,400 kPa).[54] On landing the No. 1 engine was usually shut down when taxiing to save brake wear, as keeping both engines running at idle power was still sufficient to propel the Lightning to 80 mph if brakes were not used.[55] Dunlop Maxaret anti-skid brakes were fitted.

https://en.wikipedia.org/wiki/English_Electric_Lightning

PS I have had a thought for my FL2
(70/9)squared = about 60
Does this mean that if I blow my tyres up to 60psi I can travel at 70mph without aquaplaning? FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 76k+ miles) (MY2015)

With its high landing speed and skinny tyres that makes sense, never seen any reports or stories of Lightnings aquaplaning off runways.
I knew a few RAF pilots of that era and the only problem with the Lightning was damage to the tail pipe due to the pilots attempting to get the shortest take off and rotating before the airspeed was high enough, if you stood it on its tail it had enough power to go vertical without airspeed  my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.