Maximum Tire pressure (a police perspective)

I've been going by the rating on the side of the tire for, oh, 30 years or so...

isn't the sill label for ride comfort only. I too go by what's on the tire, max 35 psi.

We've talked here before about max cold tire inflation pressure. Here's a fascinating article from Officer.com . Some police officers drive with maximum air pressure in their tires as shown on the tire sidewall, not the door sill or the owner's manual.

Here's a link to the article for some great photographs:

and here's the text in case the page is deleted in the future:

Driving Under Pressure

Proper Tire Pressure Could Save Your Life

Posted: Wednesday, December 21, 2005

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^Ã?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.

-- Sgt. Dave Storton is the Director of the San Jose Police Academy, and he holds a Master's Degree in Adult Education. He is the lead instructor for the Emergency Vehicle Operations Course (EVOC) at the San Jose Police Academy, and is a lead instructor for the local regional academy. He teaches EVOC instructor courses, advanced EVOC instructor courses, off road EVOC, counter-terrorist / dignitary protection driving, and motion picture stunt driving. Dave has trained over 3,500 drivers.

Photo courtesy of Bobby Ore Motorsports

----- Original Message ----- From: "Hachiroku ????" Newsgroups: alt.autos.toyota Sent: Tuesday, May 27, 2008 11:26 PM Subject: Re: Maximum Tire pressure (a police perspective)

Still a terrible idea. No tire company or vehicle manufacturer would support doing so (unless of course the recommended pressure is the same as the max pressure listed on the tire's sidewall).

The police officer is an idiot too. The Police Interceptors do not get the same tire placcard as the civilian Crown Victorias. They don't get the same tires either. They get extra load tires (see

. The tires aren't rated to carry any more load at 44 psi than at 35 psi, but the higher pressure is allowed for high speed driving. Exceeding 35 psi in a police car is probably a reasonable thing to do if you plan to drive at high speed for long periods of time (like a police car). However, given that a CV won't exceed 118 mph and that Michelin does not recomment increasing tire pressure above the vehicle manufacturer's recommend pressure until your speed exceeds 124 mph, I doubt that increased pressure over the recommended pressure is warranted. But even if it is a reasonable thing for a Police vehicle, this doesn't mean it is a good idea for typical civilian drivers.

Ed

=================================

Furthermore, any time I see advice like that given by the cop or some other "expert", they never mention that there are so many different tire models available, there's no way such general advice can apply to all tires. Maybe cops choose from a smaller universe of models, but the rest of us are faced with a lot more variables.

what? you'd actually trust the word of a manufacturer of automobiles over that of a policeman? With that kind of thinking, you'd probably buy diet supplements based on your physician's or dietitian's advice, and not necessarily believe the claims of the sales clerk in the health food store! For shame.

Yeah...I'm sort of partial to tire manufacturers, especially after someone from Michelin probably saved my life. 1985, bought new tires for my 82 Tercel, based on "expert" advice from the tire store. The car was hydroplaning all over the place, no matter how I adjusted the pressure. Called Michelin, and to paraphrase the guy I spoke with: "WTF? No way that tire will work on that car." He made arrangements for the right model to be shipped to the dealer immediately, and it didn't cost me a penny to get the problem fixed.

I usually only get 80-120,000 miles out of a set of tires...

Most people don't know they have to let their tires cool before they fill them... and most oil companies who fill tires dont take the time to worry about that either.

We've talked here before about max cold tire inflation pressure. Here's a fascinating article from Officer.com . Some police officers drive with maximum air pressure in their tires as shown on the tire sidewall, not the door sill or the owner's manual.

Here's a link to the article for some great photographs:

and here's the text in case the page is deleted in the future:

Driving Under Pressure

Proper Tire Pressure Could Save Your Life

Posted: Wednesday, December 21, 2005

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^Ã?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.

-- Sgt. Dave Storton is the Director of the San Jose Police Academy, and he holds a Master's Degree in Adult Education. He is the lead instructor for the Emergency Vehicle Operations Course (EVOC) at the San Jose Police Academy, and is a lead instructor for the local regional academy. He teaches EVOC instructor courses, advanced EVOC instructor courses, off road EVOC, counter-terrorist / dignitary protection driving, and motion picture stunt driving. Dave has trained over 3,500 drivers.

Photo courtesy of Bobby Ore Motorsports

There are two figures on the sidewall of every tire. " MAX pressure 44 psi at MAX load 1300 lbs." The 44 psi is for a tire loaded to it's maximum load. Tire profile is the reason why the pressure is adjusted according to the weight on the tire.

Then why do some tires wear more in the center than on the edges? Why do some tires wear more on the edges than the center?

The steel belt doesn't keep the tread flat on the road, it keeps the tread from squirming or twisting around side to side. That is the primary reason why radial tires get much better tread wear than bias-ply tires. It's also why radial tires run cooler than bias-ply.

Sorry but tire construction has more of an effect on the tire rolling over than pressure. If the tire is severely under inflated (Hydroplaning

Correct

Again he is correct.

Yes, but the proper pressure isn't the pressure listed on the sidewall of the tire unless you also are loading it to it's maximum load.

This is just wrong. Yes, they realized a cost savings in their training fleet but those cars are NOT used on the roads to train the officers. They are used on closed courses to teach defensive driving and avoidance maneuvers. They also are used to teach other driving techniques that are only rarely used on public roads. The cars are not driven at speed for 4 or 5 hours a day.

-------------------------

I drove fleet trucks (3/4 ton, 4 wheel drive pickups) for a number of years. I went through at least 10 or 12 trucks putting around 100,000 to 120,000 miles on each one. My truck tires would last from 80,000 to 120,000 miles but I did two things. I weighed each axle when fully loaded and then I put the proper amount of air in the tire for the load it was carrying. The sidewall might have listed 80 psi but my pressures were more like 65 to 70 psi. The only times I had tires fail were due to punctures or sidewall cuts (we did a lot of travel on railroad right-of-way). I maintain my personal car tires the same way, I adjust the pressure according to the load I'm carrying.

Now, before some smart-ass points it out. No, I don't adjust tire pressure as I use gas or when we buy groceries. But if we're going on a trip with a lot of luggage in the trunk, yes I will add from 3 to 5 psi to the rear tires.

A word of advise. If you use 10 minute oil changes places for oil changes, don't let them mess with your tire pressure. I've had these folks let air out of my truck tires so that I only had 35 psi in them instead of the 65 or 70 they needed.

Jack

I thought Race teams run their pressures so low so that when the tire is under load and is heated due to stress that the pressures come up to the right amount. This is why they use nitrogen in them instead of air it allows the amount of gas expansion that occurs under heating, and therefore the tire pressure to be accurately modeled under race conditions. if they set 15 psi cold it may be equal to 40 psi hot. this is why race cars have issues on cold tires. there is not enough pressure in them to perform correctly.

I have been misled by so many cartoons. Or does that only apply to large white tires on 8" rims?