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Driving Under Pressure (full article)

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Old 06-01-2008, 02:13 PM
lamebums lamebums is offline
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Driving Under Pressure (full article)

Proper tire pressure could save your life!

http://www.cleanmpg.com/photos/data/500/1133915712312_Bobby-Ore-Pic.jpg
Sgt. Dave Storton - Officer.com - December 21, 2005

Proudly debunking the PSI = POP myth. Posted because of its frequent citing by CleanMPG members. -- Ed.

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. [bolded for emphasis] 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... [Read More]

Last edited by xcel : 01-25-2009 at 04:30 AM.
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Old 08-02-2008, 07:29 AM
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Re: Driving Under Pressure (full article)

Hi Austin:

___It appears as if somebody put some pressure of their own on Officer.com and the article was updated with much of it magically missing? You did good

___Good Luck

___Wayne
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Last edited by xcel : 08-02-2008 at 08:32 AM.
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Old 11-21-2008, 08:05 AM
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Re: Driving Under Pressure (full article)

This is interesting. I bet it would be way more difficult or impossible to drive that truck on two wheels if the tire pressures were at door placard. Also regarding performance and safety, it is easy to see how running at max sidewall would probably decrease road traffic accidents by giving drivers better chance at correcting a mistake, or having a much wider margin of error before getting into a sticky situation. Prevention being better than cure kind of thing....So I wonder why don't car manufacturers recommend max sidewall then?
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Old 11-21-2008, 08:15 AM
voodoo22 voodoo22 is offline
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Re: Driving Under Pressure (full article)

As one of my best professors said, it's about money, everything is about money and the sooner you figure that out, the better off you'll be!

Hehe.

IMO lower pressure is recommended because:

it gives people a more comfortable ride and thus the perception of more quality
tires wear out faster, so tire companies make more money
you use more gas, so oil companies make more money
maybe even it increases your probability of getting into an accident which makes more money for the bodyshop
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Old 11-21-2008, 08:15 AM
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Re: Driving Under Pressure (full article)

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Originally Posted by jdhog View Post
So I wonder why don't car manufacturers recommend max sidewall then?
Two words: Ride Quality. A soft ride sells cars.
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Old 11-21-2008, 08:36 AM
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Re: Driving Under Pressure (full article)

Yeah I see. Money makes the World go around.

I wonder then which side of the fence car safety governing bodies would sit, Door placard or Max sidewall? surely if there was enough evidence of max sidewall being safer then it would be required by car manufactures to post that instead of cushy feeling psi that sell more cars and so on.....oh well. Maybe that's why new cars are coming mandatory with TPMS, but along with TPMS they should also make the public aware that max sidewall is safer than placard.
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Old 11-21-2008, 11:48 AM
WoodyWoodchuck WoodyWoodchuck is offline
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Re: Driving Under Pressure (full article)

Thank you lamebums. I’m printing a copy to share with my dealer when I go in for my 5,000 mile oil change and they deflate my tires for me.
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Old 11-21-2008, 11:57 AM
voodoo22 voodoo22 is offline
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Re: Driving Under Pressure (full article)

Quote:
Originally Posted by WoodyWoodchuck View Post
Thank you lamebums. I’m printing a copy to share with my dealer when I go in for my 5,000 mile oil change and they deflate my tires for me.
I insist that they put on my service sheet not to touch the PSI and they usually listen. Ask them to not check your tire pressure.
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Old 11-21-2008, 08:44 PM
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Re: Driving Under Pressure (full article)

My experience with higher Tire PSI so far has been surprising, at least to me.

I always believed the tire PSI listed by the auto maker was for ride comfort. But I also was of the belief that High PSI would result in a decrease in traction.

I was right and wrong.
Right in: With higher pressure ride has suffered, as I thought, in fact more than I thought it would.

Wrong in: Traction has NOT decreased, in fact it’s better. With lower (auto manufacture listed) PSI my car would under steer. Front tires losing traction before the rear.

Next question for me is: will snow and ice traction still be better with the higher PSI?
Cold pavement so far has not yet been an issue.
I had a deer jumped out in front of me, on a Cold night. I jammed on the breaks and turned just a bit in an attempt to avoid the collision. Missing the deer by less then 12inches. Traction and control was GREAT, better than I would have expected.
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Old 11-22-2008, 01:57 AM
lamebums lamebums is offline
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Re: Driving Under Pressure (full article)

The Echo's handling at door placard - for lack of a better word - sucks. It understeers easily and will chew up the outside of tires pretty quickly.

They have to be at sidewall or better at all times.

When I took my car into Tire Discounter's I told them to press up the new tire to sidewall. They did (and also let the other three down to sidewall).
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