Originally posted by snowracer69
Ok, roommate is back and here's the info he has:
This is all taken from the perspective of an airplane that is landing or taking off.
When taking off, the airplane will start to hydroplane at 9*sqrt(air pressure in PSI)... that is 9 times the square root of the air pressure in PSI. That speed is in knots, so will be different in MPH, but not much (don't want to do the math right now).
When landing, the airplane will be hydroplaning until it slows to a speed of 7*sqrt(air pressure in PSI) in knots once again. At that point, the tires will have traction and authority.
Now granted this information is related to aircraft, but I'm sure it correlates to other "tired" vehicles as well.
My roommate thinks the info came from the book "Aerodynamics for Naval Aviators" which is basically the authority on aerodynamics right now.
Oh, and the tires have nitrogen in them (99. 9% sure on this). 
Doesn't expand as much at high altitudes and low pressures.
Josh
Be careful of the (mis) information you post. The scenarios given are accurate for aircraft, but that doesn't really apply to trucks. When an A/C is landing and taking off, its effective weight changes because of the lift the wings generate.
Not so with a truck.
Here's my dissertation on the subject, as posted earlier... .
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
First of all, let me say that I am posting this in hopes that I don’t insult anyone’s intelligence. I have just read a thread where someone was talking about tall tires vs skinny tires in relation to hydroplaning, and I found that there is some misinformation out there on the exact phenomenon. If I do a good job writing this, maybe they will let me write for the TDR mag? OK, maybe not…
Hydroplaning is what happens when a tire fails to contact the road surface because it is “riding” on a wedge of water on the road. Imagine the difference between your buddy’s bass boat trolling along THROUGH the water, versus when that monster 150HP outboard has you skimming ON TOP of the water. The skimming is hydroplaning, and the variables we will discuss all play a factor in both tire hydroplaning and the bass boat scenario. Since hydroplaning occurs specifically on the tire’s contact patch, let’s look at the factors that affect traction on a wet road:
1) Width of tires -- more accurately, the surface area of the contact patch (to some extent tire height plays a role as well, since a taller tire has a bigger contact patch for a given width)
2) Axle weight—the FORCE acting on the surface area of the contact patch
3) Depth of water on the road—this determines the VOLUME of water that the tires must displace to contact the road.
4) Viscosity of the fluid displaced—i. e. a “thinner” fluid pumps easier, and therefore would be less likely to hydroplane. We assume we are talking only about water, so let’s consider this one constant.
5) Speed of vehicle—This determines the TIME available to displace the water in the contact patch.
In order for a tire to have traction on a wet road (primarily standing water) it has to first displace the water between the contact patch and the road. Because water is a viscous fluid, it tends to resist this displacement. The more water you have, the more resistance. In fact there are really only three factors that play a role in hydroplaning: pressure on the contact patch (weight on each tire divided by surface area of contact patch), the volume of water that must be displaced, and the time available to displace that water. In fact, we could write it as a formula:
(Pressure * Time)/volume= resistance to hydroplaning.
We can draw from this formula a number of conclusions:
1) the deeper the water is, the more likely I am to hydroplane (more water volume)
2) The more pressure on the contact patch, the LESS likely hydroplaning is.
3) The more time available to displace the water, the less likely hydroplaning is. (Slow down!)
This confirms what you already know—tall skinny tires tend to hydroplane less than fat tires. We can see two reasons for this. First, the wider tire has to displace MORE water. Second, the wider contact patch has LESS pressure on it since weight has stayed the same (P=F/A) This is a “double whammy”.
This isn’t the only way to decrease the chances of hydroplaning. The formula tells us we can drive a heavier vehicle or slow down. But if we increase the efficiency with which the tire displaces water, then the TIME required to displace it decreases, and we are less likely to plane out. This allows us to either decrease vehicle weight or increase speed safely as a result.
Finally, the SHAPE of the contact patch has a role in hydroplaning. For a given area, say 15 square inches, a longer, narrower contact patch is better than a short wide one. Why? Because the majority of the water displacement is done by the leading edge of the patch only (picture our bass boat and its bow). The rest of the contact patch gets a “free ride” along behind the leading edge that already displaced the water. Thus, a narrower leading edge slices better through the wedge of water.
Go ahead and run the biggest tires you wish. Just remember the physics that is taking place at your tires’ contact patches and SLOW DOWN!! (or add a bunch of weight, or run narrow tires, or……. .
~~~~~~~~~~~~~~~~~
In the above post, I neglected to mention the effect of taller tires (wich tend to increase the size of the contact patch for a given width). Other than that, it's still pretty relevant.
You can read the whole thread
here
Attention: TDR Forum Junkies 
Left lane wasn't much better. 
