Driving Under Pressure (full article)

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

  1. 94_2300inLa

    94_2300inLa Member

    Im running 50 and happy atm. Thanks for the replys ill. Ill watch for buldges.
  2. gjsullivan

    gjsullivan New Member

    Thanks for the info. I just bought a 2007 Prius touring with 41K miles. It had new replacement tires that came with car, Hankook Ventas V4se, 195/55/R16 ( Standard size for Prius Touring ) . These were highly rated performance tires, not LRR tires. and they were at 35 F, 33 R. I was getting 38 to 39 mpg. Very disappointing as my 05 Prius got 48 around town and up to 53 on the highway, but that did have Michelin Energy Saver A/S 195/65/15.

    I put the pressure on the Hankook Ventus up to 49 / 45 lbs. ( also installed an Optima Yellow top battery and cleaned the MAF sensor ) and now my mileage is up to 45.1. This is winter driving, so factoring in the winter penalty of 3 to 4 mpg, I am right where I would expect to be.

    The ride is stiffer and is definitely noisier on the highway, especially when on pavement the has been roughed up by tires with studs.
  3. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    3-4 MPG ? What planet are you living on ? Okay , I see that you're in Oregon , where it doesn't get cold like Chicago. Here it's more like an 8-10 MPG hit.
  4. srivenkat

    srivenkat New Member

    Is it legal to go with the Max sidewall pressure instead of the door label pressures? How will this affect insurance claims (life and auto)? Thanks in advance.
  5. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    Ho boy. I don't think anyone here wants to give legal advice. I WILL tell you that I run sidewall max (44psi on mine) during the summer. Safe alert driving means MUCH less need for insurance. YMMV.
  6. CapriRacer

    CapriRacer Well-Known Member

    Starting off: I am not an attorney. I am a tire engineer who has been involved in some litigation and has talked extensively to lawyers who do this sort of thing. Take what I am about to write in that light. Knowledgeable, but not definitive or authoritative.

    First, there are very few laws concerning what an owner of a vehicle can or can not do - and it varies considerably. Most of the laws are directed at shops and repair facilities. A good example of this is that emissions equipment is not allowed to be disabled BY A SHOP (and there are penalties for this), but an individual owner can not be fined for this. However, that owner may have trouble getting his vehicle to pass emissions testing.

    There are no regulations about what inflation pressure an individual owner can use.

    - HOWEVER -

    It is always possible for there to be a lawsuit - and these potential lawsuits are sometimes characterized as having the force of law.

    A good example is if a tire shop applies a tire with a lower speed rating - and there is an accident. It is possible for the tire shop to be sued because of their actions.

    So, to answer your question: It is possible for an individual owner to be sued if he deviates from the car manufacturer's specified inflation pressure - and some would say this has the same effect as a law - but I am not aware of any regulation on the subject.

    It is also possible for insurance companies to deny coverage in situations where the vehicle is being operated in non-standard ways.
    Last edited: Oct 16, 2014
  7. srivenkat

    srivenkat New Member


    Thanks for the reply. It seems to me it should be easier to argue against Max Sidewall being a factor in an accident (unless the tire blew or caught fire) than it is to argue against Under Inflation (below door label) as a factor.

    Do you agree?

    Thanks in advance.
  8. CapriRacer

    CapriRacer Well-Known Member

    If I were advising an attorney on the subject, I would point out that a tire that is near the max sidewall pressure is much, more more likely to have been deliberately done so - that a tire inflated under the placard pressure is more likely to be the result of neglect - a common issue with vehicles. I would think an attorney would interpret that the highly inflated tire was a willful act and that might make it worth pursuing a lawsuit.

    And just so we are clear, I think this is a remote possibility.
  9. ksstathead

    ksstathead Moderator

    Yes, the driver at max sidewall deliberately improved fuel economy, handling in most situations, tread life.

    But it is true that if they can prove that inflating consistent with tire manufacturer specs caused an accident, then either the driver or the manufacturer could be help to account. Just as Ford and Firestone were liable for the gross underflation on the Explorers.

    There are no cases have heard of where inflating to max sidewall caused anything worse than increased noise, vibration, and harshness (NVH).
  10. CapriRacer

    CapriRacer Well-Known Member

    Just to get the facts absolutely straight. NHTSA did NOT cite the inflation pressure as a cause of the problem in the Explorers. Others have pointed the finger in that direction, but the facts don't support that conclusion.

    Au, Contrare!


    Note the "Dynamic Bruise Resistance". Admittedly the link is to an old paper, but that doesn't make the facts reported wrong.
  11. ksstathead

    ksstathead Moderator

    Wrong again, Capri.

    The problem was above max sidewall.
  12. CapriRacer

    CapriRacer Well-Known Member

    Sorry, but not all the data points were above max sidewall. I merely quoted the smallest and the largest pressures tested, but the trend is quite clear.
  13. xcel

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

    Hi All:

    Many of the European OEMs have a range of pressures for increasing load. A BMW 3-Series moves from 36 to 49 psi with 1 person to 3 and a load of golf clubs in the trunk.

    Recent RAM 1500 ECOdiesel with 17" Goodyear Wranglers was placarded at 40 psi all around unloaded. Max sidewall was 44 psi IIRC? Can someone look that up at TireRack. I am on a smartphone just about ready to board a ship.

  14. brick

    brick Answers to "that guy."

    OEM Wrangler HPs are indeed rated at 44psi. However, TireRack has another version of the same tire rated for 51psi in the same size and same load rating. The only difference I can see is that the one with the higher sidewall pressure weighs a pound less. Odd.

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