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Tire Pressure


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53 replies to this topic

#41 OFFLINE   jdbob

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Posted 14 March 2015 - 06:52 PM

I personally set my C-Max tires at 43 PSI at 68F, near sea level.  

 

The compressor that comes with the car has dual calibrations, PSI and Bar. I just set mine to 3 Bar, which is 43.5 PSI.

 

tire_inflation.jpg









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#42 OFFLINE   engnrng

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Posted 14 March 2015 - 08:02 PM

OK, so let's say you leave in the morning with the tires cold at 51 psi and the air temp at 60 degrees. You take the long way and eventually drive to 7000 feet where the pressure increases 3 psi, add another 2-3 psi for heat from friction and 3 psi for a 20 degree increase in ambient temperature from AM to PM, now your tire pressure is at 60 psi, 12 pounds above what Ford recommends and 9 pounds above the tire manufacturer’s maximum rating. You better not hit that pot hole or have to make a moderate to high speed emergency maneuver. But hey, you saved a half mile of battery energy or .10 gallons of gas, so why wouldn't you do it.

Your sarcasm is noted.  In the interest of fact:  even a 40 degree F increase in ambient temperature would cause a pressure increase of less than 1 psi.  If friction and heat from high speeds, frequent braking, and hard cornering causes another 40 degree increase in the air temperature inside the tire (assuming you have fully insulated your wheel rims), that might increase another 1 psi or so.

 

Of course, knowing there would be a 3 psi increase in internal tire pressure due to elevation change, the smart driver might start 3 psi lower than their normal.  Do you drop your 38 psi to 35 psi in anticipation of the climb?  Probably not, but if I was at the top end, 51 psi, I might drop it to 48 psi before I started, particularly if I was planning to do a lot of hard cornering and high speed driving over 125 mph or so with 3 or 4 adult passengers.  In fact, the higher the tire pressure, the less the temperature inside the tire increases with load and speed (DOT HS 810 561).  The tires on my 2014 C-Max are V rated, so I will not go faster than 149 mph.  I promise. 



#43 OFFLINE   rbort

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Posted 14 March 2015 - 08:14 PM

The imperial way of calculating the pressure was really funny!   :hysterical:

 

I just checked my tires, they are at 50 to 51psi at the moment.  I'm driving south to AL, should I take the pressure checker with me and see what they are at over there compared to here at 40 degrees warmer?

 

Checked the oil, right on the end of the hash marks at the top end.

 

Charged the battery, showing 25 miles range, up from 22 (rock bottom) in the dead of winter.

 

Gas tank is full since January when the prices dropped to $2 a gallon, showing 634 miles range, total 659 with battery.

 

GOOD to go!

 

-=>Raja.


Edited by rbort, 14 March 2015 - 08:39 PM.


#44 OFFLINE   GaryG

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Posted 14 March 2015 - 08:22 PM

OK, so let's say you leave in the morning with the tires cold at 51 psi and the air temp at 60 degrees. You take the long way and eventually drive to 7000 feet where the pressure increases 3 psi, add another 2-3 psi for heat from friction and 3 psi for a 20 degree increase in ambient temperature from AM to PM, now your tire pressure is at 60 psi, 12 pounds above what Ford recommends and 9 pounds above the tire manufacturer’s maximum rating. You better not hit that pot hole or have to make a moderate to high speed emergency maneuver. But hey, you saved a half mile of battery energy or .10 gallons of gas, so why wouldn't you do it.

 

I could care less if your hard head can't except saving money on tires, saving your life on your cars handling or getting better MPG. You have that right! I think if you listen to the experts here on this board, and you should try and see for yourself.

 

Gary


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#45 OFFLINE   timwil56

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Posted 15 March 2015 - 01:42 AM

 I think if you listen to the experts here on this board

 

Gary

WOW! What makes you an "expert" other than meeting Wayne Gerdes?


Edited by timwil56, 15 March 2015 - 03:30 AM.


#46 OFFLINE   GaryG

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Posted 15 March 2015 - 07:29 AM

WOW! What makes you an "expert" other than meeting Wayne Gerdes?

 

Lets face it, you're afraid to try something you have never tried. Wayne recommends you slowly increase your tire pressure a little at a time till you feel a little more at ease. As the San Jose Police Dept. says, just telling someone about improved handling doesn't always work. However, letting the student drive the training course with the recommended tire pressure by Ford, and then raising the tire pressure to see the improvement themselves work.

 

Gary 



#47 OFFLINE   engnrng

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Posted 15 March 2015 - 10:17 AM

WOW! What makes you an "expert" other than meeting Wayne Gerdes? 

Direct observations by experienced operators can be valid, particularly with respect to a vehicle like the C-Max (narrow track, 50 series aspect ratio tires, 50/50 weight distribution).  Both drdielsel1 and Gary (and several others) have demonstrated their observation and analysis abilities and their conclusions have often been supported by others.

 

If you want information from recognized pneumatic tire experts, you and other forum readers can locate and read DOT HS 810 561, February 2006, sponsored and published by NHTSA.  It is the scientific and engineering authority for tire design in the US on THE PNEUMATIC TIRE.  Members of the editorial board include people from US DOT, Goodyear, MIchelin, Cooper, and several universities.  From the Preface:

 

"The chapter authors are recognized authorities in tire science and technology.  They have prepared scholarly and up-to-date reviews of the various aspects of passenger car tire design, construction and use, and included test questions in many instances, so that the book can be used for self-study or as a teaching text by engineers and others entering the tire industry."

 

From chapter 5:  "...the pressures shown are considered minimum for the corre­sponding loads shown. Higher pressures for high speed and other special circumstances are often recommended by vehicle and/or tire manufacturers and are acceptable as long as they do not exceed the maximum pressure marked on the passenger car tire."

 

Let me restate my position:  I am not making a recommendation of 38 psi or 51 psi as being optimum for everyone, since that depends on a number of factors.  I am saying that between 38 psi and 51 psi is legal and safe.  Opinions from this engineer:  If you carry passengers and personal gear, higher pressures above 38 psi are appropriate.  If you want to decrease heat due to the sidewall flexing and lengthen the life of the tire, higher pressures above 38 psi are appropriate.  I personally run my tires at 51 psi and thus do not feel the need to have to pull out my inflator every time I add a passenger or go to Costco.  I am also getting even tread wear across the face of the tire, an indication that the tire inflation I am running is suitable to my driving environment and style.  A good indicator of tire performance is wear.  The best indicator is driver confidence in control.  For the surfaces and speeds at which I operate, I perceive no loss of control with my tires at 51 psi, so I am comfortable with that inflation pressure.


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#48 OFFLINE   drdiesel1

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Posted 15 March 2015 - 12:48 PM

Direct observations by experienced operators can be valid, particularly with respect to a vehicle like the C-Max (narrow track, 50 series aspect ratio tires, 50/50 weight distribution).  Both drdielsel1 and Gary (and several others) have demonstrated their observation and analysis abilities and their conclusions have often been supported by others.

 

If you want information from recognized pneumatic tire experts, you and other forum readers can locate and read DOT HS 810 561, February 2006, sponsored and published by NHTSA.  It is the scientific and engineering authority for tire design in the US on THE PNEUMATIC TIRE.  Members of the editorial board include people from US DOT, Goodyear, MIchelin, Cooper, and several universities.  From the Preface:

 

"The chapter authors are recognized authorities in tire science and technology.  They have prepared scholarly and up-to-date reviews of the various aspects of passenger car tire design, construction and use, and included test questions in many instances, so that the book can be used for self-study or as a teaching text by engineers and others entering the tire industry."

 

From chapter 5:  "...the pressures shown are considered minimum for the corre­sponding loads shown. Higher pressures for high speed and other special circumstances are often recommended by vehicle and/or tire manufacturers and are acceptable as long as they do not exceed the maximum pressure marked on the passenger car tire."

 

Let me restate my position:  I am not making a recommendation of 38 psi or 51 psi as being optimum for everyone, since that depends on a number of factors.  I am saying that between 38 psi and 51 psi is legal and safe.  Opinions from this engineer:  If you carry passengers and personal gear, higher pressures above 38 psi are appropriate.  If you want to decrease heat due to the sidewall flexing and lengthen the life of the tire, higher pressures above 38 psi are appropriate.  I personally run my tires at 51 psi and thus do not feel the need to have to pull out my inflator every time I add a passenger or go to Costco.  I am also getting even tread wear across the face of the tire, an indication that the tire inflation I am running is suitable to my driving environment and style.  A good indicator of tire performance is wear.  The best indicator is driver confidence in control.  For the surfaces and speeds at which I operate, I perceive no loss of control with my tires at 51 psi, so I am comfortable with that inflation pressure.

Again..... :worship:  Great information and thanks for posting it  :shift:


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#49 OFFLINE   ptjones

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Posted 02 February 2016 - 02:51 PM

I just talked to the Michelinman Concierge Service and I told him that I was interested in the contact patch area change from 38 to 50psi of my Michelin Energy Saver A/S tires.  He said he didn't know even know how to get that info, but the important thing was to get even tire ware across the tire which gives the maximum tire contact patch.  He said the Michelin Energy Savers have a 55K warranty and I told him I was using 50psi and got 64K mi. out of my first set and 58k mi. on my second set so far. On my first set there was only 1/64" difference in ware from the outside edge to the inside edge which he said was very good and recommend keep using 50psi in the tires! smile.png

So there you have it, Michelin rep recommends 50psi! smile.png BTW his # is 1-888-633-3339.  Also most members wouldn't notice a difference between 38 and 50PSI in their tires so try it out and let us know what you think. smile.png  

 

Paul



#50 OFFLINE   drdiesel1

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Posted 02 February 2016 - 07:10 PM

 

I just talked to the Michelinman Concierge Service and I told him that I was interested in the contact patch area change from 38 to 50psi of my Michelin Energy Saver A/S tires.  He said he didn't know even know how to get that info, but the important thing was to get even tire ware across the tire which gives the maximum tire contact patch.  He said the Michelin Energy Savers have a 55K warranty and I told him I was using 50psi and got 64K mi. out of my first set and 58k mi. on my second set so far. On my first set there was only 1/64" difference in ware from the outside edge to the inside edge which he said was very good and recommend keep using 50psi in the tires! smile.png

So there you have it, Michelin rep recommends 50psi! smile.png BTW his # is 1-888-633-3339.  Also most members wouldn't notice a difference between 38 and 50PSI in their tires so try it out and let us know what you think. smile.png  

 

Paul

 

Where was the 1/64 difference. As in what area was worn more ? Thanks! Center area or edge area.



#51 OFFLINE   bschwerdt

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Posted 03 February 2016 - 01:12 PM

I just got caught up on this thread, thanks to the recent posts pushing it to the top of the new content.  Definitely an amusing (and sometimes heated) discussion.  I'm amazed at how civil this board stays compared to certain others I frequent ( ::ahem:: mynissanleaf ::ahem:: ).

 

Everything I've read or observed concurs with the conclusion that the door jam should be treated as a minimum and the sidewall as a maximum.  And BTW, that refers to cold tire pressure.  So driving up a tall mountain, creating heat from driving and changing ambient pressure not to mention changing temperatures during the course of the day - these things are all accounted for.  The tire can handle a higher pressure than 51 PSI.  But if you start higher than that when cold, you may exceed the maximum pressure during the course of your day.

 

FWIW, I keep my tires around 45 PSI, and I notice a 5-10% difference in MPG between 38 and 45.  I have not measured on a very controlled course, but rather rely on the law of averages (as in, the average economy over one or more tanks of gas).

 

P.S. I got a good laugh out of the imperial definition of PSI.  I love it!


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#52 OFFLINE   ptjones

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Posted 03 February 2016 - 02:11 PM

Where was the 1/64 difference. As in what area was worn more ? Thanks! Center area or edge area.

It was a year and a half ago so i'm not sure whether it was the inside or outside edge, but the center was between the too. :smile2:

 

Paul



#53 OFFLINE   jdbob

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Posted 03 February 2016 - 02:49 PM

P.S. I got a good laugh out of the imperial definition of PSI.  I love it!

 

I was surprised by a recent video by TeslaBjørn showing a group of Tesla owners stopping at a petrol station in Norway to make sure their tires were properly inflated before a long trip. And they were measuring in PSI!


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#54 OFFLINE   drdiesel1

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Posted 03 February 2016 - 07:53 PM

I just got caught up on this thread, thanks to the recent posts pushing it to the top of the new content.  Definitely an amusing (and sometimes heated) discussion.  I'm amazed at how civil this board stays compared to certain others I frequent ( ::ahem:: mynissanleaf ::ahem:: ).

 

Everything I've read or observed concurs with the conclusion that the door jam should be treated as a minimum and the sidewall as a maximum.  And BTW, that refers to cold tire pressure.  So driving up a tall mountain, creating heat from driving and changing ambient pressure not to mention changing temperatures during the course of the day - these things are all accounted for.  The tire can handle a higher pressure than 51 PSI.  But if you start higher than that when cold, you may exceed the maximum pressure during the course of your day.

 

FWIW, I keep my tires around 45 PSI, and I notice a 5-10% difference in MPG between 38 and 45.  I have not measured on a very controlled course, but rather rely on the law of averages (as in, the average economy over one or more tanks of gas).

 

P.S. I got a good laugh out of the imperial definition of PSI.  I love it!

51 is the rated max and the tire will carry more. They're designed with a specification and a safety margin too.


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