Driving Under Pressure (full article)

Discussion in 'Articles' started by lamebums, Jun 1, 2008.

  1. Damionk

    Damionk DWL Lover

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

    CapriRacer Well-Known Member

    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.
     
  3. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    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
     
  4. featherfoot

    featherfoot Well-Known Member

    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.
     
  5. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    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.
     
  6. CapriRacer

    CapriRacer Well-Known Member

    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!
     
  7. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    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.
     
  8. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    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’

    [​IMG]
    Fronts at 101K.

    [​IMG]
    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
     
  9. CapriRacer

    CapriRacer Well-Known Member

    The point was: That was my explanation.
     
  10. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    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
     
  11. CapriRacer

    CapriRacer Well-Known Member

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

    [​IMG]


    Have I accurately portrayed these?
     
  12. FSUspectra

    FSUspectra Practicing true conservatism!

    I would say xcel is in the camp of shoulder wear at placard pressure.
     
  13. 94_2300inLa

    94_2300inLa Member

    So if my max cold psi is 44 on my uniroyal liberator a/t 225/70/14r.

    Should I try 50 or higher or 48 or so?

    THanks
    Brian
     
  14. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Super Moderator Staff Member

    My personal view is that you should gradually increase pressure and see how they behave. Different tires behave differently at different pressures. You need to ensure you feel safe. My Prius' OEM Yokohamas could get a bit skittish around the max sidewall (44) while my FuelMax (51) feel fine at 47.5. A big thing to look for is even tread wear, which suggests the tire has good contact with the road.

    There are diminishing returns to raising tire pressure. The main thing is not to allow pressure to drop low.
     
  15. Gord

    Gord Super Moderator Staff Member

    Good advice INATM. I started at placard and went up 3psi at a time over a period of months.
    Max sidewall on my Michelin Energy Savers on front is 51, currently running at 58.
    Bridestone on rear, max 51, running at 50.
     
  16. ALS

    ALS Super Moderator Staff Member

    Michelin MXV4 Energy's on my Volvo are a handful in the rain at any pressure above 42 psi, side wall is 44 psi max. I have zero problems with the Prius running Michelin Energy Saver A/S max sidewall of 44 psi.
     
  17. CapriRacer

    CapriRacer Well-Known Member

    To try to put this in perspective: What pressure does the vehicle tire placard call for?
     
  18. 94_2300inLa

    94_2300inLa Member

    Thanks everyone, ill try a few more psi.
     
  19. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    What INATM said. And pay attention to handling and braking traits for each higher pressure you go to. Rain and snow ; you may have to back off to a lower pressure and do some informal testing (braking and steering) to make sure the car still responds the way you expect it to.
     
  20. phoebeisis

    phoebeisis Well-Known Member

    Comfort-
    that is why the door pressure is selected.
    Door placard is safe- and comfortable
    Occasionally the manufacturers have gone too far in the comfort direction
    The Ford Explorers 20 or so years ago
    Pretty much destroyed Firestone-great USA Corp
    Ford put placard at 26-27 psi-pretty low for radial tires on a 4500 lb vehicle
    Bad ending of course-blowouts roll overs deaths
    They all learned their lesson from that.

    I go with very close to sidewall now
     

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