Maximum Tire pressure (a police perspective)

On Tuesday, May 27, 2008 8:09:02 AM UTC-7, Built_Well wrote:
> 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:
>
> http://www.officer.com/article/artic...on=19&id=27281
>
> and here's the text in case the page is deleted in the futu
>
> 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'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

Thanks for re-posting my article. That was back from 2005. I have recently updated it to answer many of the questions and comments that article generated.
http://www.thedrivingcompany.com/dri...-pressure.html

On Thu, 26 Jun 2014 14:01:47 -0700 (PDT), wrote:

>On Tuesday, May 27, 2008 8:09:02 AM UTC-7, Built_Well wrote:
>> 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:
>>
>> http://www.officer.com/article/artic...on=19&id=27281
>>
>> and here's the text in case the page is deleted in the futu
>>
>> 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'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
>
>Thanks for re-posting my article. That was back from 2005. I have recently updated it to answer many of the questions and comments that article generated.
>http://www.thedrivingcompany.com/dri...-pressure.html


I was surprised that the high pressure didn't cause problems but
looking at other reports it does seem that some vehicles and tires do
ok at pretty high tire pressures. While googling around I found this
http://www.performancesimulations.co...on-tires-1.htm
which was a pretty interesting report on actual tire contact area
versus tire pressure. Results are nothing like expected.

Ashton Crusher > wrote:
>
>I was surprised that the high pressure didn't cause problems but
>looking at other reports it does seem that some vehicles and tires do
>ok at pretty high tire pressures. While googling around I found this
>http://www.performancesimulations.co...on-tires-1.htm
>which was a pretty interesting report on actual tire contact area
>versus tire pressure. Results are nothing like expected.

Don't guess, measure. It doesn't take a lot of effort to chalk up your
tires and drive around a bit.

Also notice that lateral stiffness will increase as you add air pressure,
and that may actually make more of a change in handling on some tires with
larger sidewalls than the change in contact area.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."