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Driving Under Pressure: Editorial & Features at Officer.com



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.

 

I will add if you run side wall pressure (like I do), make sure you check the tire pressure hot, as they will increase in pressure.
I'll guess the bashers of this item on here will find some other reason to not, but heck who cares if the keep it to thereself and not spread bogus information.

 

I'm sorry but i'm not a fan of running max tire psi. And the few pros do not outweigh the cons.

BUT i do agree with pcs0snq, i'd check the psi at the tire's hottest temperature... just to be more safe.

 

your tires will not wear less, they will wear more in the center of the tire

 

Thank you. It's about time someone realized this.
Rep for you.

 

Obviously neither of you read the article. With a steel belt, this is not possible. It is a myth.

 

I agree that it's likely a myth. Anyone have any hard data one way or another, please post. Until then, it's all opinion.

My views align with what's in the article. I'm currently running 42 in my minivan and Fit and 40 in my Saab. I may go higher on the Fit since those tires are rated into the 50's. The minivan and Saab are rated at 44 max. I've only been doing this for a couple of weeks so I don't have any hard data or experience yet.

My Saab has other front suspension issues so I won't use that as an example though.

 

I read an article somewhere on tirerack's website that stated that the max pressure on the sidewall was a cold pressure (in other words fill it to that when its cold, there is allowances for the expanding air as it heats up).

 

I'm don't think the article is wrong, but it's not totally right either. The tire's profile shape and width comes into play.

My skinny 185/65/14 stock tires on my old Civic sedan had a curved profile. Most performance oriented tires are pretty square.

I autocrossed my Civic sedan in HS for 2 seasons. I had to run high tire pressure to keep the tire from rolling onto the sidewall. The 2 highest worn areas were the center and the edge of the tire were the tread and sidewall meet.

With the tires natural curved profile and narrow width, pumping up the pressure put more load on the center. The effect is less pronounced or non existent with a stiff sidewall, wide performance tire.

 

good article. me likey.

 

So tire rack or some www sourse is saying you can exceed the side wall list tire pressure when the tire is HOT and subject to the most issues. It's BS and anyone would be a fool to trust that advise

 

You people seem to be missing the big picture here. We are talking about a Crown Victoria. Not exactly the peek of performance. Basically a car that was donated or given at a cheap negotiated contract price from the manufacturer. Hence it needs all the help it can get, regardless of being a cop car or not.

Other than that thanks for the info. Good article but info sounds a little dated, I'll stick to what the car manufacturer says and not the tire manufacturer.

 

Not really. The pressure on the side wall is the maximum cold pressure at the maximum rated weight. Yes the tire heats up and pressure goes up but this is allowed for by the design of the tire with safety margin. Not sure how else you would do it in the practical sense. If you put the max hot rating on the tire, how would you expect someone to measure that - how much driving to achieve max pressure? what ambient pressure? What road The choice to make it cold is a little arbitrary because it isn't based on a specfic ambient temperature either but it is practical because one is more likely to measure the tires before driving rather than driving for a while then stopping to measure.

One would be more foolish to issue a product to the consumer with small safety margins. Safety margins should be added to make sure only a fool could hurt himself - it should be clear the fool well exceeded the design parameters before something catastrophic occurred. Lawyers and lawsuits factor heavily in the design of consumer products for just this reason. Variations in manufacturing drive safety margins out even further.

I heard a story about twenty years ago when I lived in Hawaii about a kid who was killed pumping up an automobile tire. The story was he believed since auto tires are beefier than bike tires, they should be inflated higher than bike tires. Bike tires easily exceed 80-100 psi. The auto tire exploded killing the kid. Might be urban legend, who knows.

 

Yes indeed, agree on all counts. I'll even add another; a Crown Vic -- especially a loaded up police special Crown Vic -- will heat its tires faster, and to a higher temperature, than any Fit ever will -- INCLUDUNG tracked Fits.

Which brings us to this.
Exactly the wrong conclusion. You need to look at it from the perspective of the tire manufacturer. He has to be extremely conservative with what gets printed on the side of the tire. It's a safe number.

 

Not buying it, sir
Do your tires say anything about HOT or COLD on the listed "MAX Press" side wall?
Never seen that and that's why it's not at some specific temperature.

Pressure is a function of temperature and the idea is do not exceed the side wall pressure listed at any temp. Most users do not inflate to max they use the door jam figures. As we are talking about using Max for Eco reasons and being an engineer, I just figured I'd suggest to measure them hot, to make sure they do not exceed tire spec's. It's what I did and was not a big deal.

BTW The Dunlap Sport OEM tires at rated at 1102lb's at 51psig.
That's 4408lb max to tire rating
My M5 Sport weight (according to Honda) is 2471lb
11 gal of gas is 70lb
1867 payload.... for tires
Page 147 of my 2008 owner manual says 850lb max hmmmm seem to of last 1000lbs

 

No one is posting THEIR PSI levels. GOGOGOGO!

I'm at 32, moving up to 45 when I get my pressure guage in the mail

 

I'm running 42 in my minivan and Fit. 40 in my Saab. The minivan and Saab are rated at 44, Fit in the 50's somewhere.

 

No problem.

Not sure what the numbers were intended to say but the load limitation is the suspension, not the tires. You'll bust the springs before you bust the tires.

 

I'm still not hopping on the max pressure bandwagon. I'll stick with what the manufacturer suggests indicated on the sticker placed in the driver side door jamb. I'm not going to argue over it.

 

haha, I get to play spoiler

I counter with the NHTSA recommendations
(National Highway Traffic Safety Administration)

Tire Safety, Brochure (DOT HS 809 361 October 2001)

Also another great source for tire safety information;
Safercar.gov

Also here is an interesting quote from that write up, suggesting that maybe not all police officers agree with running max PSI in their tires.
Bottom line is that auto manufactures and anybody actually liable for when things go wrong basically say no.... people who like to push limits say it is ok. It leaves the whole air pressure question in limbo... what is the best air to run? lol