What's the best front/rear-'tire pressure' for a long road trip?

Discussion in 'Gen 2 Prius Main Forum' started by ski.dive, Jul 25, 2019.

  1. ski.dive

    ski.dive Active Member

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    What's the best front/rear-'tire pressure' for a long road trip?
     
  2. sam spade 2

    sam spade 2 Senior Member

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    Whatever the sticker on the door says.
    Measured "cold"; that is at the start of the day before driving........which might not be really cold this time of year.
     
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  3. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    I've got 3 stick gauges and one cheapie digital. The readings they give are all over the map. I suspect the digital and one of the sticks are closest. However, my favourite is another one of the sticks, just because it's easier to use and read. That one appears to read 3 psi high. I use it, and set psi 3 pounds above target.

    For setting pressures: I go a pound or two above the sticker in the door, and use the front pressure for all four.
     
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  4. WilDavis

    WilDavis Senior Member

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    I tend to go a couple above what's on the door, and check every week or so… …and also check for tread wear!

    I have wireless-monitors¹ on the caps, and note that at this time of the year the pressure when cold (early morning) can vary as much as 5-6 lbs difference to that shown after the car has been sitting in the sun all day!

    ¹
     
  5. audiodave

    audiodave Active Member

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    Posted via the PriusChat mobile app.
     
  6. bisco

    bisco cookie crumbler

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  7. PriusCamper

    PriusCamper Senior Member

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    The stickers on the door and the ratings on the tire are PSI ratings for the absolute lowest, slowest and safest performance for liability reasons... This is the tire pressure you want an accident prone village idiot to drive with and still win a liability lawsuit if that dumb clueless mistake-based person files a lawsuit against you.

    In general, the more tire pressure, the faster the responsiveness of the tire and the less rolling resistance/higher MPG until once you get up past 50psi and the tire will become so fast you'll lose traction and notice the tires slipping as you accelerate from a stop light or while accelerating up a roughly paved curving road.

    For best results, bring a pump with you on your trip and experiment with increasing PSI by a pound or two until you boost it too high and then back it off.

    For long freeways drives in hot summer weather at 70mph range I prefer 47psi in front and 45psi in the rear, then I back it off a few pounds in wet winter weather. But I'm using LRR Ecopia tires and my main goal is maximizing MPG not driving fast, not hard cornering, just slow lane speeds and saving money.

    Also if you plan on driving long distances on gravel or unpaved roads reduce tire pressure back to the upper 30's and drive slow because on unpaved roads the faster you drive, the more likely you'll get a flat tire.

    Also the most notorious tire pressure moment was an LSD-fueled Hunter S. Thompson going on an all expense paid by his publisher research trip for his next book that became a hug hit: Fear & Loathing in Las Vegas:

    Screenshot from 2019-07-25 14-38-45.png

    Read the rest here: phscollectorcarworld: Lost Star Cars: Hunter S Thompson's Fear & Loathing in Vegas with Cadillac DeVille
     
    #7 PriusCamper, Jul 25, 2019
    Last edited: Jul 25, 2019
  8. sam spade 2

    sam spade 2 Senior Member

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    BUT......also note that he mentioned some disadvantages to doing that.......and it needs to be said that you should NEVER inflate cold to a pressure higher than the max. shown on the sidewall.

    Also doing that with some brands of tires will result in wearing out the center of the tread a LOT faster than the edges and will make them more prone to hydro-planing in a sudden rain storm.

    Overall, it might cost you a LOT more than the few MPGs you save with the higher pressure.
     
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  9. fuzzy1

    fuzzy1 Senior Member

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    That is too vague a question, as the answer depend at lot on your own personal preferences not expressed here.
    All the hydroplaning research I've seen, particularly the NASA and other aviation links posted here long ago, indicate that higher inflation pressure uniformly reduces hydroplaning.

    The empirical conclusions were that hydroplaning onset speed is proportional to the square root of inflation pressure. The more pressure, the faster you can go before it hydroplanes. Other factors will guide your max pressure.
     
    #9 fuzzy1, Jul 26, 2019
    Last edited: Jul 26, 2019
  10. PriusCamper

    PriusCamper Senior Member

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    Same old song of obedience without question... Tires are not like balloons in terms of uneven wear if over-inflated... That's just a myth obedient people that always follow PSI specs think up so other people will be as unquestionably obedient like them and they'll feel better about it that way.

    Truth is there's plenty of commenters on Prius Chat over the years who suggest over-inflation slows down tire wear due to less friction/more nimble moving tire over pavement... A sluggish 35psi creates more tire wear not less!!! And I confirmed this directly. My tires were rated for 60K miles and for the entire life of the tires they were at 48-45psi and I got 75K miles out of my tires before they started slipping in the winter weather.
     
  11. fuzzy1

    fuzzy1 Senior Member

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    Most brands of steel-belted radial passenger tires do not do this, because they use a non-rubberized version of steel for those belts just barely under the tread. These steel belts stretch very very little, so the center doesn't have the flex to balloon out.

    We have seen a very very few reports of excess center wear, but without enough detail to track down what really happened.

    The old bias-ply tires clearly did balloon out and suffer excess center wear. Any radial tires with belts made of something other than steel, or with inadequate amounts of steel, might also be susceptible to this.
     
  12. sam spade 2

    sam spade 2 Senior Member

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    Aviation tires are nothing like car tires.
    And......thin hard tires are much less likely to hydroplane......but their overall traction is greatly reduced too so the hydroplaning becomes a secondary consideration unless you drive in water ALL the time.

    IF....you increase the pressure enough to reduce the contact patch.....especially if it raises the side edges of the tread and pushes out the middle.......it will indeed increase the tendency to "fly" over the water.

    Those who choose to ignore the recommendations of the "experts" who build things thinking that they know more.......are often disappointed in one way or another........because there almost always is some kind of trade-off.
     
  13. fuzzy1

    fuzzy1 Senior Member

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    I remain unaware of any meaningful differences with respect to hydroplaning.
    Raising tire pressure doesn't make the tread thinner or its rubber tread layer harder.

    I remain unaware of documentation showing that greater pressure reduces overall traction. Long before your time here, one poster did refer to a particular research paper to support this claim. But a careful reading of its definition of terms revealed that said poster had misread the paper, it didn't say what he initially thought it said.
    Not ALL the time, just 152 days per year. Haven't you ever heard that Seattle is rainy and wet?
    [​IMG]

    Wet traction is a more difficult and hazardous case than dry. So treat wet as the primary case, dry as secondary. If we prepare for wet, and always drive like it is wet, then the dry conditions take care of themselves, with no surprises. (Well, apart from the much less common icy surprises.)
    Raising the side edges and pushing away the middle, is an excellent description of the contact patch photos of the underinflated tests, not the higher pressure tests, in a study linked here long ago.
    I have always acknowledged that this issue involves trade-offs. When making these trade-offs, the manufacturers weight ride comfort very heavily, far more so than some of us here would like. We would like to increase the weighting of other performance factors, and are willing to reduce the weighting of this ride comfort factor.

    Other people don't feel the same way about these trade-offs. Fine, pick your own personal balance, this is clearly a matter where personal preference matters. Just don't try to BS your way through with a bunch of old unsupported mythology.
     
    #13 fuzzy1, Jul 27, 2019
    Last edited: Jul 27, 2019
  14. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    For sure ride comfort, because a teeth rattling test drive doesn't help sales. And on the other hand, mpg. Maybe they also weigh suspension and bearing life?

    At the end of it all, maybe spec, or a few pounds higher at most, is the sweet spot? I just don't see the typical owners aims being that different than the manufacturers'.
     
  15. sam spade 2

    sam spade 2 Senior Member

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    Just because you are unaware of something does not mean that it doesn't exist.
    Pointless argument.
    I quit.
     
  16. fuzzy1

    fuzzy1 Senior Member

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    You can help make me aware of such literature.

    Or you simply keep making claims with no support, as is your normal style.
    I'll take that as an admission of no documentary support.
     
    #16 fuzzy1, Jul 27, 2019
    Last edited: Jul 27, 2019
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  17. Raytheeagle

    Raytheeagle Senior Member

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    I just wish he’d listen to himself when he says he quits;).

    Removes the only member off my ignore user list(y).
     
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  18. sam spade 2

    sam spade 2 Senior Member

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    Anyone who really cares about this......or any other subject for that matter.......can do a Google (or similar) search and find a LOT of really good information about tire pressures and hydroplaning.

    Those who are more concerned with beating me up than actually learning something will just rant on.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    Excellent idea. Here are some starters, including some of the original long-ago research. If anyone digging deeper than I did into these finds any hint that increased inflation pressure ever increases hydroplaning susceptibility, please flag it to me:

    https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640000612.pdf
    https://static.tti.tamu.edu/tti.tamu.edu/documents/147-2.pdf
    https://static.tti.tamu.edu/tti.tamu.edu/documents/147-3F.pdf
    https://vtechworks.lib.vt.edu/bitstream/handle/10919/75183/final_paper_REVIEW.docx?sequence=1
     
    #19 fuzzy1, Jul 28, 2019
    Last edited: Jul 28, 2019
  20. Skibob

    Skibob Senior Member

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    Whatever you normally use for tire pressures will be more than adequate.
     
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