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Proper tire pressure could save your life! (cleanmpg.com/forums/showthread.php?t=11652)

http://www.cleanmpg.com/photos/data/500/1133915712312_Bobby-Ore-Pic.jpgSgt. 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. 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.

[b]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... http://www.officer.com/web/online/Editorial-and-Features/Driving-Under-Pressure/19$27281

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

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?

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

So I wonder why don't car manufacturers recommend max sidewall then?

Two words: Ride Quality. A soft ride sells cars.

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.

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.

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.

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.

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).

Hey guys. First post here. Question on this topic:

I've heard, and this may be unsubstantiated, that increased tire pressure increases drag in the struts by forcing a strut movement on a small road impact where a softer pressure in the tire wouldn't have been able to force that movement (and the impact taken up by the sidewall of the tire). I know from experience that increasing tire pressure improves rolling resistance, but the thrust of what read was saying that there's a point of diminishing returns as well...that once you get high enough, you're not doing any more good for rolling resistance, and you may be bringing on unintended negative consequences as well.

Any truth to that?

I feel there is some truth to it. BUT!

I think you would be hitting some dang big bumps before it would more of a negative impact then the lower rolling resistance of the higher PSI.
I would recommend keeping the PSI up before worrying about it.



Now along that line. Finding the smoothest line down the road with the lease amount of car directional adjustment also improves FE.

There has been a time or 2 when in a glide and catching up to slower traffic instead of using the break I will look for a rougher track in the road (like the crack at the edge) and ride that a sec or 2, the rougher surface will give you a gentile slowdown.

i could not agree more about tire pressure. my experience has been the same. better handling, taction, and no hydroplaning. and of course much higher fe and looong tire life. at 75-85psi its been very nice .

Hi All,

I am in Ireland and motoring is a bit different here! Most cars are small/medium sized with manual transmission and there are very few hybrids.

I have been thinking about how driving style affects fuel consumption ever since my father used to coast down hills and have come up with a few conflicting principles.

I also ride a motorbike and this has raised some issues for me regarding furl consumption. My bike (F650GS) is a single with fuel injection and it normally does around 55mpg (imperial) around town. On the highway cruising at around 70mph, my consumption increases to over 70mpg. This raise two issues with me:

1. Bikes are not very aerodynamic and I would expect the consumption to worsen with increased speed. I understood the resistance increases exponentially with speed. So why does the consumption increase?

2. Cars here should return around 30-40mpg. A car is considerably heavier than a bike but returns the same mpg as a mid-size or large bike.

Weight and aerodynamics are the two big factors influencing consumption but there seems to be some conflicts in what actually happens. Any explanations?

The other area that occupies my mind concerns engine efficiency. My bike provides maximum power/torque at about 4000rpm. Is this the figure that returns the highest mpg? In my car I always thought that the lowest rpm would give the best mpg.
I figure now that this depends on whether you want constant speed (in which case lowest rpm), or if you will be changing speed a lot such as in traffic or perhaps going uphill (in which case max torque rpm).

I hear often that you should reduce speed to improve consumption. For my bike 70 mph seems good -so I should actually speed up!!! However, for my car I am not sure by how much. On the principle that resistance increases with speed, then I should drive really slow. Obviously 10mph wont result in good consumption as it would take a lot of time to cover the journey. So just what is a good efficient speed? 30mph? 40mph? 50mph? I know this depends on the car the conditions etc, but if they can generalise that 60 is too high then there must be a general speed figure to aim for. What is it?

Anyway it is good to see that there are other people out there who are concerned with MPG instead of BHP.

Cheers

So just what is a good efficient speed? 30mph? 40mph? 50mph?

As I like to simplify;
Holding the accelerator on the floor wastes a lot of gas, but idling wastes even more as your not going anywhere.

Usually your highest/longest gear will give the best economy. At what speed do you get the best? As you say, it would depend heavily on the car. For my HiHy, between 45 & 50 gives me the best mileage I can get on flat ground with no wind while holding a steady speed. With a tail wind, my best economy may be as high as 55. With a head wind, maybe as low as 40. Downhill...speed doesn't really matter as I can just coast pretty much for free at any speed the car wishes to reach. For a typical uphill, I think around 40/45 is best, but since there are few places where I can play with my speed while maintaining the same climb, its pretty much a guess.

The best way to find out its a monitoring device that can show your instant mpg. Set you speed and watch the gauge for a minutes. Bump the speed up or down and see if the mpg improves or gets worse. However, as you see all over the site, there are techniques that offer far better economy than just setting a best speed and holding it.

Has anyone tried asking the publisher or author to post the entire article again?

........

1. Bikes are not very aerodynamic and I would expect the consumption to worsen with increased speed. I understood the resistance increases exponentially with speed. So why does the consumption increase?

..........



The problem is how you are measuring the consumption.

Stop and go traffic results in idle time - and as was pointed out, this only consumes fuel without generating distance.

If you really want to compare what speed does for consumption - without the effect of idling - then you need to drive the same road at different speeds.

Thanks for this article, really cleared a few things up

Just curious,

What is the effect of alternates to air in tires, and their impact on mileage. Is this bunk?

Some claim a 4-10% difference (Something I have a hard time believing):

Has anyone tried this, and did it make ANY difference?

Hi infitom:

___N2 will not help and when it heats up, its pressure increase is less which will give less FE over air. Low moisture content is good but air is usually free... Or close to it and has been working fine for well over one-hundred years ;)

___Good Luck

___Wayne

Since there has been a lot of talk lately of tires and pressure I thought I would bump this.

Since there has been a lot of talk lately of tires and pressure I thought I would bump this.

It is indeed unfortunate that the article has some gross errors in it. Had Sgt. Storton gotten those right, he might have come to different conclusions and the tone would have been completely different - and not useful for the high pressure arguement.

Hi CapriRacer:

Gross errors? Please explain since in my 123,000 miles using the same Michelin’s at 60 psi experience, I would say there are few gross errors at all. Of course the wear across my Michelin's is still even all the way across after all those miles which is not what I could say for anyone running at placard and then below the instant they drive off?

How long have your latest tires lasted? How long has any of your tires lasted?

All told, right to the point and dead on. Even BMW recommends 49 in their 3-series with 4-onboard.

Wayne

it doesn't make sense for the car to recommend tire pressure because the orig tires wear out. it should tell the owner to go by what the tire says. also; i was overfilling my tires (around 37psi) and one of them developed a bulge on the tread. some tires can probably take higher psi but the cheapie tires cannot.

it doesn't make sense for the car to recommend tire pressure because the orig tires wear out. it should tell the owner to go by what the tire says. also; i was overfilling my tires (around 37psi) and one of them developed a bulge on the tread. some tires can probably take higher psi but the cheapie tires cannot.

My general principal in life is to go with the cheap option unless there's a good reason to do otherwise. Things like shoes, phones, computers, etc, I usually go cheap and replace sooner. Tires are one place where I spend the money for quality.

First: What was the point of Sgt. Storton’s article? What was he advocating?

He was advocating the use of 44 psi in tires used on police pursuit vehicles. He was making no recommendations about ordinary cars and SUV’s.

- And he had a valid point, but he arrived at it the wrong way.

When police pursuit vehicles are used in pursuit mode – which they are sometimes asked to do at a moment’s notice– the use of higher inflation pressure in the tires reduces the heat build-up due to the speed – and that has safety implications. Further, higher pressures improve the responsiveness to steering input – very helpful for emergency maneuvering.

But Sgt. Storton tried to address the common counter-arguments to this position – and unfortunately got his facts wrong.

1) At the time that he wrote the article (2005), Police Pursuit Crown Victorias came with P225/60R16 97V tires with a placard pressure of 35 psi. These tires would have been labeled with a max pressure of 51 psi (in order to qualify for the V speed rating) – contrary to what the article says.

2) At the time, civilian Crown Victorias came with P225/60R16 97T’s with a placard pressure of 32 psi – contrary to what the article says.

3) If put in terms of load carrying capacity, the Police Pursuit versions would have almost 400# more! – contrary to what the article says.

4) The load carrying capacity of these types of tires maxes out at 35 psi – contrary to what the article says.

So his argument concerning load carrying capacity is wrong.

He then tries to address another common counter-argument – Wear:

5) Increasing tire pressure does cause changes in the curvature of the tread face – and more importantly in the pressure distribution – contrary to what the article says.

6) The steel belt does not prevent this – contrary to what the article says.

But to be fair, the steel belt RESTRICTS this growth – and more importantly, the tires specified for police pursuit vehicles will have another layer of fabric on top of the belt – commonly called a cap ply – which further restricts this growth.

It would have been more effective for the article to mention that the effect this amount of pressure increase would have on tire wear is pretty small compared to the effects produced by things that normally cause wear issues – such as alignment, hard cornering, etc. – and that it is unlikely to cause any major issues – and THEN cite the experience of the San Jose Police department.

7) The issue with the Ford Explorer was the tires – not the wear on the tires - contrary to what the article says. The tires were recalled, not the vehicle. If you want a more detailed analysis, I go into that here:

http://www.barrystiretech.com/fordfirestone.html

I am not even going to bother to discuss trick driving and why Bobby Ore uses high pressures (Hint: It makes the trick possible!)

The article could have been written in a different way, making it technically and factually correct, and be just as persuasive in arguing for the use of 44 psi in Police Pursuit vehicles.

So that’s why I said it had gross errors.

Oh, and by the way, the reason BMW recommends 49 psi in their 3 series is for the same reason Sgt. Storton was advocating for 44 psi – high speeds!

My personal experience contradicts your comments on wear at high pressures. Placard pressure = worn out edges. Max sidewall pressure = even wear across the tread. Multiple sets on multiple vehicles.

Hi CapriRacer:

A given specific spec tire was the only tire ever placed on a CrownVic police cruiser? I know the Volt was spec’ed with an exacting GY Assurance FuelMax tire (the 500 – A –A) and by build # 900, some are equipped with (580 – A – A) GoodYear Assurance Fuel MAX’s.

05 Accord – Original Michelin MXV4 Plus’

http://www.cleanmpg.com/photos/data/2/Accord_Fronts_at_101_000_miles.jpg
Fronts at 101K.

http://www.cleanmpg.com/photos/data/2/Accord_Rears_at_101_000_miles.jpg
Rears at 101K.

They are now 6-years old and have over 120k on them now. Fronts are just now into the 2 to 3/32 range. Rears are still 4 +.

Your point was?

And now that I have shown you mine at 100+ K, mind showing me yours ;)

Wayne

...........Your point was?.........Wayne

......Gross errors? Please explain..........Wayne

The point was: That was my explanation.

Hi Capri Racer:

The real point was my pictures... If you would like, I can go take some at 123K if you want them. Just let me know when you have pics of any of your own your own at 100K + miles while running placard whenever you reach it. Doubtful that they exist but I may as well ask?

Wayne

Hi Capri Racer:

The real point was my pictures... If you would like, I can go take some at 123K if you want them. Just let me know when you have pics of any of your own your own at 100K + miles while running placard whenever you reach it. Doubtful that they exist but I may as well ask?

Wayne

I suspect we are talking about different things - and perhaps the best way to explain that is with a matrix:

http://i1134.photobucket.com/albums/m606/capriracer1/wearmatrix.jpg


Have I accurately portrayed these?

I would say xcel is in the camp of shoulder wear at placard pressure.