Tire Sidewall blown after psi raised to 34

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by gboss, Apr 4, 2022.

  1. Merkey

    Merkey Active Member

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    I love the look of those 17 inch rims, but they do come at a cost in MPGs.
     
  2. PaulDM

    PaulDM Active Member

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    Isn’t the pressure written on the side wall the maximum that that tyre will take, not the pressure meant for your car ? 60 psi sounds a tad high.
    I’m running 35-37
     
  3. fuzzy1

    fuzzy1 Senior Member

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    The sidewall maximum pressure seems to be the maximum rated cold pressure, and seems to have plenty of margin built in to accommodate changing ambient and operating temperatures and elevation (mountain passes have reduced atmospheric pressure, which increases the observed tire gauge pressure).

    It isn't the maximum pressure the tire will take before bursting, but burst pressures are generally not disclosed. 'Rumors' among hypermilers put burst pressures up in the triple-digit range, so 60 psi (or more) isn't all that uncommon among the really hard core who don't have dental fillings to rattle loose. If any are bursting at that level, they aren't surviving to get the words of warning back to us. ;)

    No undamaged passenger car tire should be blowing anywhere near the OP's 34 psi.
     
  4. PaulDM

    PaulDM Active Member

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    Good luck with that
     
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  5. johnHRP

    johnHRP Member

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    60 PSI tires can be considered a felony. It endangers everyone on the road. It is like 4 rolling bombs on the highway. 35-40 Psi is the optimum pressure for Prius. It accelerates the wear of all suspension parts, especially bushings on control arms, trailing arms, and struts/shocks too. For the amount of negligible fuel, you pay way more on safety, comfort, and worn parts.
     
  6. Paladain55

    Paladain55 Junior Member

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    Nah not that serious. You can go on Youtube right now and see people pumping tires up to blow them up but it takes like 200 psi. But there is almost no gain above 45psi. Most of the Teslas recommend 45 psi as well for maximum range. I've been doing 50psi on all of my large sidewall vehicles. Keeps me from rolling the sidewall and eating the side of the tires so much and gives me better wear.
     
  7. PaulDM

    PaulDM Active Member

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    I guess your not running standard tyres then. Here’s a guide for the rest of us …
    662C4254-7247-4C72-BF64-22D4C7E4E1ED.jpeg
     
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  8. Paladain55

    Paladain55 Junior Member

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    I realize what the tire load rating system is. Just because you pump the extra air into the tire doesn't mean you can safely increase the load rating of the tire, the tire will still be rated for x load at spec psi etc...
    I am saying you don't have to follow the spec psi. You can go to the max sidewall and the car will be fine. A couple %+ in mpg between 30 and 45 but almost no gain in % after 45.
    Tires will be fine at max sidewall if that is what you prefer is all i am saying.
     
    #68 Paladain55, Apr 29, 2022
    Last edited by a moderator: Apr 29, 2022
  9. PaulDM

    PaulDM Active Member

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    I don’t agree with that offensive comparison.
     
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  10. johnHRP

    johnHRP Member

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    Obviously. Large Torque EV cars like Tesla or Porsche need higher tire pressure. The same thing with large load SUV and truck. The tires are made differently with thicker sidewall, unlike Prius tires. It is just ridiculous pumping Prius tires above 40 psi. It is just completely dumb. The ride quality is so bad.
     
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  11. fuzzy1

    fuzzy1 Senior Member

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    The practitioners of it claim excellent luck, including longer and more even tread wear.

    I've never tried anything above 40-something, I wish to retain a number of dental fillings. I do know that the 26 psi label on the door jamb of a couple of our cars -- one past, one still present -- did lead to premature hydroplaning and uneven tire wear. Bumping up to 35 fixed those problems and improved MPG.
    Not sure why it would be a felony. Underinflated tires are proven more lethal, and yet that hasn't been made a felony. All TPMS systems are built to warn of underinflation, but most don't give any warning on the high side.

    As for accelerated wear of suspension components, in my direct discussion with a performance car enthusiast who was on here until a couple years ago, he dismissed such concerns as FUD, but wasn't going to make waves by arguing it out in public. His assertion was that all of this stuff on a Prius is negligible compared to the stresses commonly put on performance cars.

    I'm not in a position to judge between these conflicting claims.
     
  12. johnHRP

    johnHRP Member

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    Underinflated tires do not cause any explosion and are often caused by unintentional leaks or road hazards. Overinflated tires are almost always deliberate acts and endanger others on the roads. My friends and family had exploded tires on the roads all of them were caused by overinflated tires at high speed/interstate. Some Franchise shops did not read the recommended pressure on the door jams and just pump it to 40psi or more.

    The wear and tear on suspension parts are not an instant process. It takes many years to develop and overinflated tires accelerate it a lot. You can feel how rough the ride is when the pressure is above 35psi in Prius. My old 02 Altima with 16" wheel has 29Psi recommended pressure and it is way better when I pump it at 29, not 35 like most shops did.

    Toyota engineers know the proper specs of the tires pressure on their cars and trucks. I don't think we are better than Toyota engineers in terms of specs on tire pressure.
     
    #72 johnHRP, May 2, 2022
    Last edited: May 2, 2022
  13. PaulDM

    PaulDM Active Member

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    Often people forget that “cold tyre pressure” increases by 4-5 psi once the tyres have warmed up ( in temperate zones ) more in hot conditions like California Summers.
    Draw from that what you will.
     
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  14. jdenenberg

    jdenenberg EE Professor

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    Toyota engineers do know, but the spec is a compromise between comfort and performance by marketing. The marketing people go for comfort over performance. Besides, Toyota does not know the characteristics of the replacement tires on your car and the tires that I buy are stronger than the OE tires and have a higher Max Sidewall PSI (51). I run my Nokian tires at 42/40 (front/rear) to get a bit more MPG, better handling, and more even tread wear. You can, of course, make your own decisions.

    JeffD
     
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  15. johnHRP

    johnHRP Member

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    I agree, the ideal tire pressure also depends on the tire brands. With Goodyear Performancegrip2, 225/45T17 summer tires in Auris/Corolla IM hybrid, 36-39 psi is still comfortable and good handling, just like what Toyota recommends. With older Dunlop tires, the ride is indeed too harsh above 36psi, I can feel all the crevices on the road. 42 or 40 psi is not excessive and some tires are still comfortable at that pressure. But pumping at 50 or 60 psi is outside human sanity level.
     
  16. fuzzy1

    fuzzy1 Senior Member

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    Underinflated tires commonly overheat and experience blowouts, which some would call 'explosions'. In the Ford Explorer / Firestone Tire debacle, in which underinflation was one of several contributing factors, these blowouts killed over 200 people.
    Over the years here, I just haven't found any meaningful figures for crashes from overinflated tires. Can you point me to some?

    All the figures and estimates I've seen are for just the underinflated ones.
    Very many of us here in PriusChat received our Gen3 Prii from the dealership with tires set at 40 psi. This pressure was set at the factory, supposedly to prevent flat-spotting or other problems during their Pacific Cruise to North America, and our dealerships failed to reduce them to the door placard recommendation during PDI. Many of these drivers also did not lower the pressure to recommendation, yet I heard of no reported problems other than harsh ride.

    Then the Gen4 Prii came along, and many drivers here reported their cars arriving with 50 psi. Still no problems beyond harsh ride.
    Can you say "Ford Explorer"?

    Tire inflation pressure is a weighted compromise between conflicting goals. Vehicle manufacturers typically place very heavy weighting on ride comfort. Numerous drivers prefer to optimize for a different weighting of these factors, commonly with less on ride comfort and more on some other factors. It took me several years to figure out that the door placard recommendation on my household's Honda and Acura was too low for my tastes and wet climate safety.

    Then along came the deadly Firestone / Ford Explorer debacle, where it was determined that the vehicle manufacturer's label recommendation (the exact same psi as our Hondas) was too low, and was one of several factors contributing to that era's Explorers suffering high rates of blowouts and lethal rollovers. That cemented my loss of absolute faith in those car manufacturer door labels. Ever since, I've felt absolutely no guilt or qualms in increasing pressure for crisper control, improved hydroplaning resistance, and longer and more even treadwear.
     
    #76 fuzzy1, May 2, 2022
    Last edited: May 2, 2022
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  17. fuzzy1

    fuzzy1 Senior Member

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    Note also that when climbing from sea level to high Colorado mountain passes and plateau roads, ambient air pressure drops by 5 to 6 psi. But (apart from temperature changes, see Ideal Gas Law), tire interior volume is effectively constant, so absolute tire pressure doesn't change. Therefore, the gauge pressure that we read -- the difference between inside and outside absolute pressure, and also the working pressure that holds the vehicle up -- increases by this 5 or 6 psi.

    I've never seen any mountain driving advice to reduce tire pressures in order to avoid excessive inflation. That must mean that tire labels and recommendations are meant to accommodate both this and the operating warm-up factors.
     
    #77 fuzzy1, May 2, 2022
    Last edited: May 2, 2022
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  18. johnHRP

    johnHRP Member

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    35 psi front 33 psi back, 40 psi is probably fine when it is fully loaded with 4 passangers and luggages.
    Defective tires are often the cause of tire explosion. These days, we rarely have underinflated tires because most cars have tpms. If the maximum rated pressure on tires 50 psi, it does not mean we can pump it to 50 psi.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    I noticed labels with different tire inflation recommendations for different loads on rental cars in Europe, but that doesn't seem to be the practice in the U.S. market. Does that mean tires and cars behave differently in the U.S. than in Europe? Or are the customers different and need simpler instructions?
    Are you sure that your friends and family that experienced exploded tires, didn't already have damaged or defective tires?
    There are still plenty of pre-TPMS cars still out on the road, so I don't believe underinflated tires are yet "rare".

    And this forum has as seen a fair number of drivers ignoring the TPMS, or operating just at the bare minimum to avoid alerts, and repeatedly getting caught when temperatures dip a bit. That alert threshold, when set at factory default, is still 'underinflated', just not as severely as when at common blowout levels.
    Why would a tire that cannot safely be pumped up to 50 psi, have a sidewall cold pressure label rating of 50 psi? Full well knowing that pressure will rise a bit higher as it gets up to normal operating speeds on sun-baked pavement during heat spells, and when climbing tall mountains. That sounds like a major product liability problem.

    It may not be what the vehicle manufacturer intends for their vehicle's designed comfort and handling and performance levels, but it shouldn't be a problem for the tire itself.
     
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  20. johnHRP

    johnHRP Member

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    I talked about Prius 3rd gen and up which have TPMS. The first explosion that my friend had was a new set Primewell inflated above 40 psi and hit a nail on i-10 at 75mph. The 2nd one was a poor college student who pump a cheap Chinese tires at 42 psi in his Sentra 99. He pumped to maximum pressure because he feels it deformed too much at 34 psi. It exploded on FL State road at 55mph after hitting some gravels on the road.
    Yes, tire brands matter and offcourse pumping at max pressure 50 psi cold will eventually above 55 psi in the highway. I don't think any good tires will spontaneously exploded even at 150% maximum tire pressure. Overinflated amplifies the effect of road hazzards and defective tires.
     
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