Higher pressure stops hydroplaning??? I'd sure welcome some documented proof of this. If that's truly the case I guess I can start running my "street slicks" at higher pressure and not have to worry about driving in the rain anymore...although I suspect it would be difficult to convince the DOT of this. I was always under the impression that it's the tread design that minimizes (but never stops) hydroplaning.

I don't think anyone questions the adverse effects of running LOW tire pressure - especially the heat damage that can result. Even so, who's ever heard of breaking the bead running anything but incredibly low pressure such as with off-road vehicles where 5-10 PSI is the norm? I seriously doubt that the CHP ever popped a bead running normal (the manufacturer's spec?) pressure without hitting a curb or equivalent no matter how hard they drive. Many autocrosser's do increase their tire pressure slightly over the manufacturer's spec to improve steering response, but the key word here is "slightly". Yet in other racing venues lower pressure is preferred.

 

Here you go.
From: http://www.nhtsa.dot.gov/cars/rules/...8/part5.6.html

Skidding and/or loss of control from hydroplaning

The conditions that influence hydroplaning include speed, tire design, tread depth, water depth on the road, load on the tires, and inflation pressure. At low speeds (less than about 50 mph), if your tires are under-inflated, you actually have more tire touching the road. However, hydroplaning does not occur very often at speeds below 50 mph, unless there is deep water (usually standing water) on the road. As you get to about 55 mph and the water pressure going under the tire increases, an under-inflated tire has less pressure in it pushing down on the road and you have less tire-to-road contact than a properly inflated tire as the center portion of the tread gets lifted out of contact with the road. As speed increases to 70 mph and above and water depth increases due to a severe local storm with poor drainage, the under-inflated tire could lose 40 percent of the tire-to-road contact area compared to a properly inflated tire. The higher the speed (above 50 mph) and the more under-inflated the tire is, then the lower the tire-to-road contact and the higher is the chance of hydroplaning.

Tread depth has a substantial impact on the probability of hydroplaning. If you make a simplifying assumption that the water depth exceeds the capability of the tread design to remove water (which most likely would occur with very worn tires), then an approximation of the speed at which hydroplaning can occur can be estimated by the following formula:

Hydroplaning speed = 10.35 x inflation pressure [25]

Under this assumption of water depth exceeding the capability of the tread design to remove water:

At 30 psi, hydroplaning could occur at 56.7 mph

At 25 psi, hydroplaning could occur at 51.8 mph

At 20 psi, hydroplaning could occur at 46.3 mph.

This is presented to show the relative effect of inflation pressure on the possibility of hydroplaning.

 

Here's an article from Officer.com about tire pressure.
http://www.officer.com/article/artic...on=19&id=27281


SGT. DAVE STORTON
EVOC Contributor
Officer.com


How many officers check the tire pressure on their patrol car on a regular basis? We all seem to be great at checking that the lights and siren work, because the time to find out they don’t work is not when you get a Code 3 call. Likewise, the time to find out your tire pressure is too low is not when you are in a pursuit and trying to take a corner at high speed.

What is proper pressure?

The proper tire pressure for the Police Crown Victoria is 44 psi. If you look on the sidewall of the tire, you will see that it lists 44 psi max pressure. Regardless of what vehicle you have, use the maximum pressure listed on the sidewall. Higher pressure results in better performance, decreased tire wear, and it lessens your chance of hydroplaning at a given speed. This number on the sidewall lists “the maximum amount of pressure you should ever put in the tire under normal driving conditions.” Pursuits and Code 3 responses are not “normal driving conditions.” Many agencies maintain tire pressure at 35 psi since this is what is listed in the owner’s manual and on the door placard. The reason the owner’s manual lists 35 psi is because we get the same manual as the civilian version of the Crown Victoria. The police version, however, is fully loaded with communications equipment, a cage, and your gear. You are not looking for a soft and cushy ride, you want performance.

Myths about pressure

Let’s put to rest some common misconceptions. The tires will not balloon out creating a peak in the center portion of the tread when tire pressure is above 35 psi. There is a steel belt that prevents this from happening. Also, you are not overstressing the tire with higher pressure, and the tire will not be forced off the rim with higher pressure. The picture above is Bobby Ore of Bobby Ore Motorsports driving a Ford Ranger on two wheels. The tires on the left side have 100 psi in them, and they happen to be tires and rims from a 1999 Crown Victoria! This is a dramatic example of how pressure holds the tire in shape, and how much stress a tire can handle.

Performance

If you were able to watch a tire as it travels across the ground at high speed, you would see that it deflects to one side during cornering. The faster you are going through a corner, the more tire deflection you get. As the tire deflects over onto the sidewall, you get less traction and more of a tendency to understeer or oversteer. This could spell disaster when negotiating a corner at high speed during a pursuit or a Code 3 run. Higher pressure keeps the tire from deflecting onto the sidewall as much, which keeps more of the treaded portion on the road.

A good demonstration for EVOC instructors is to have students drive a high-speed course in a vehicle with 32 to 35 psi. Then have them run the same course with 44 to 50 psi in the tires. The student will experience a marked difference in performance. Having officers experience this difference in vehicle performance is much more effective than just telling them to check their tire pressure.

Hydroplaning

When a tire rolls across a road covered with water, the tire tread channels water away so the rubber remains in contact with the road. The factors that affect hydroplaning are speed, and water depth. Conventional wisdom says that vehicles will hydroplane in as little as 1/16th of an inch of water. Not so coincidentally, legal tread depth is 1/16th of an inch.

Tire manufactures and the Association of Law Enforcement Emergency Response Trainers International (ALERT) have shown that tires have more of a tendency to hydroplane when pressure is low. This happens because the tire footprint (the portion of the tire actually in contact with the road) is larger. For those of you who water ski, think of which is easier to get up on: a fat ski or a skinny ski. More tire surface in contact with the water makes it easier to hydroplane, just as it is easier to water ski on a fat ski. Also, a soft tire can be pushed in more by the pressure of the water on the center portion of the tread. This results in less rubber in contact with the road.

Tire wear

Much better tire wear results from maintaining proper pressure. Tires with lower pressure will wear off the outside of the tread faster from the deflection of the tire during cornering, and the tires will heat up more from increased road friction. This is one of the factors that caused the failure of a certain brand of tires on Ford Explorers some years ago. In 1999 the San Jose Police Department realized a significant cost savings by increasing the pressure in the training fleet to 50 psi. They soon followed up by increasing the pressure in the patrol fleet to 44 psi. For liability reasons, most agencies are reluctant to exceed the maximum pressure listed on the tire for actual patrol vehicles, but they reap the cost saving when going to 50 psi on training vehicles.

Next time you inspect your vehicle, make sure you check your tire pressure since your ability to performance drive is significantly affected by it. You are not driving to the store to get a loaf of bread! You may be called upon to chase a dangerous criminal or respond to assist another officer in trouble. You don’t wonder whether or not your gun is loaded before you hit the street; don’t’ wonder whether your tire pressure is correct once the pursuit starts. Check your tires routinely, just as you do with all other critical equipment.

 

As a very quick reply - low tire pressure - hydroplaning - the very tread that is designed to carry away the water is squeezed together, thus more tire is in contact with the road (there is your slick) fewer channels to carry the water away. More pressure - the tread stays open, less actual tire print but more channels to direct the water away.

 

THANK YOU for providing information from documented sources instead of based primarily on opinion being passed off as "fact"...although I did notice they reference the "relative effects of pressure" as opposed to saying higher pressure totally stops hydroplaning...and I couldn't agree more with that.

One thing I do find surprising is how they state that running higher than the recommended pressure doesn't result in abnormal wear of the center portion of the tread. I'm personally not in a position to either support nor dispute this since I'm not an expert on the subject, but why does EVERYT tire manufacturer's website that I've visited state that it does result in abnormal center wear? (I'm one who follows the vehicle manufacturer's spec and have yet to experience any uneven wear by doing so). I do find it quite surprising that the tire manufacturers themselves aren't aware of and continue to support this "Myth about pressure". The tire manufacturer's websites I've visited also mention reduced vehicle control when running with higher than recommended pressure. I can't help but wonder why there's such a difference in recommendations between the tire manufacturers and the Highway Patrol.

Thanks again!!

 

For the FEH, note that the tire manufacturer says 44 lbs and the Vehicle manufacturer says 35 lbs....?

MM

 

Same as the Crown Victoria's mentioned in the police cruiser article in this thread.

(I'm still running at 35psi. Considering increasing by at least 5 psi, and that article is some good food for thought.)

 

In my personal driving of over 300,000 miles and several sets of tires, and considering my whole family's 1,000,000 miles and dozens of sets of tires ( over the past 30 years ) I have never EVER seen a tire wear out from the center of the tread. EVER!

The tires, always, EVERY TIME wear out at the edges first, even when kept at the car manufacturer's spec (usually 35 psi ) and rotated about every 10k miles.

Even with 44psi, I'm still, really, truly, expecting the edges to wear out first.

Good topic for Mythbusters, but I don't know who has the time or patience to do 70,000 miles of wear for a TV show.

Thanks MMooney for the link and reference.
This follows common sense and my personal experience.

Why the myth?
A. Tire manufacturers WANT to sell you more tires sooner. Sounds like a good profit booster to me. ( you can make a 100 year light bulb for twice the price of a 1 year light bulb, but what light bulb company wants to sell a 100 year light bulb? )

B. Car manufacturers WANT you to use a lower pressure, so you get a softer, more comfortable ride, making their car feel more luxurious, and giving it higher reviews. If I just had a Kidney transplant, I'd probably soften my tires. But the FEH is a "truck" and I'm in good health, so I'll take the benefits of higher pressure.

FYI... with 44-49psi in the FEH, it "coasts" in EV mode about 50% farther.
I can go 2.5 miles over level ground in EV from one battery charge.
I also get 48 MPG at 48 MPH and 42 MPG at 60 MPH over level ground.
Sounds like the effect is more than "slight" to me.
-John

 

For those wondering if its dangerous to put too much air in your tires... (after all I'm one of the ones that reignited this ) This article that appears to be for police officiers, is pretty interesting.

http://www.officer.com/article/artic...on=19&id=27281

Have a look... Is this the authoritative answer? Got me... but I offer it to read.

Incidentally. I think the reason tires wear out on the edges is that when you are turning the edges do most of the work.

 

Opps.... Sorry MMooney. You'd already posted that link. I spotted it elsewhere and ran back here to post it (since I had helped re-ignite the debate).... didn't look back to see you'd beat me to it.


Its pretty interesting... and I just might be willing to try it now.