What PSI do you keep your tires in and have you seen noticable MPG improvement?

Discussion in 'Gen 2 Prius Fuel Economy' started by yossi, May 4, 2021.

  1. yossi

    yossi New Member

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    I just got an 08 with 179k and the dealer told me to keep the tires at 32psi. I read here many keeping it at 40-45. Do you see improved MPG with the higher pressure? Are there downsides to higher pressure, like loss of handling, etc?
     
  2. bisco

    bisco cookie crumbler

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    44f/42r, no noticeable difference, but i don't have to top them up as often :D

    the rides a bit harsher, maybe shortened suspension wear? no way to really know.

    dealers will tell you to follow the book, but many report leaving service with values ranging from 20-50psi :rolleyes:
     
  3. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    I used 40f / 38 r on my Gen 2, to get best tire life. MPG was not worse, might have been better.
     
  4. lexidium

    lexidium Member

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    I use 40f/38r because it was recommended on here but there's no noticeable difference from when I used 38/35 and the mileage is the same.
    It probably just means that I don't have to use the pump quite as often.
    You'll probably find that the pressure gauges are not that accurate anyway.
     
  5. srellim234

    srellim234 Senior Member

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    38/36 here. Tried going over 40 but the harsher ride was not comfortable. I figured it was not helping the suspension components either. The factory settings give the softest ride but not very good gas mileage compared to a little higher pressure numbers. 32k miles on these Yokohama Avid Ascend GT Tires and they're wearing evenly. They still have plenty of tread life on them.
     
  6. fuzzy1

    fuzzy1 Senior Member

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    Ignore the dealer, read the placard on the driver side door pillar. Doesn't it say 35 front, 33 rear? (Unless you have a model trim with larger tires.) Take that as a minimum. And remember that it means cold pressure, i.e. in the morning before warmed up from driving.

    On prior cars, I found slightly better MPG with higher tire pressures, so have never run 'just' the manufacturer recommendation on my Prius. But mpg improvements from higher pressure are not large, and many people don't like the tradeoffs, particularly the harsher ride. And there is no consensus on certain other factors such as traction and treadwear patterns.

    "Best" tire pressure is a tradeoff between conflicting goals, and different people weight those goals differently, so you'll have to make your own judgement.
     
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  7. Uberfast

    Uberfast Junior Member

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    40. Psi. For about 4 years. Nice ride
     
  8. GabrielD

    GabrielD Member

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    Speaking about psi, can someone explain what means red and black values on this Techstream screenshot?
    later edit:
    I read better, now I know what means... with red is actual pressure, with black is treshold pressure...
    One thing to mention, I inflated wit 230 psi, and the sensor read is 330 psi...
     

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    #8 GabrielD, May 7, 2021
    Last edited: May 7, 2021
  9. Valiant V

    Valiant V New Member

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    After figuring out which model 2017 we had, and which tires, AND whether we had no spare, a space-saver, or a full size spare - we figured out the correct tire pressure for our 2017 model is 36F, 35R. (and yes, the "old" trick of reading the placard on the door frame is quicker than using the manual!)

    Found out the dealer sent it out the door with 30PSI all the way around. Pretty sad since they put a new set of tires on this pre-owned car.

    We've driven a couple of hundred miles with the 30PSI. Not a bad ride (for our area) and not TOO noisy (again, very rough road surfaces here) and have been getting 60+ mpg on most trips.

    Boosted the tires to ~ 35-1/2 front and rear his morning - dead cold. (as Lexidium mentions - tire pressure gauges are unlikely to be lab quality)

    Ride seems about the same. Noise is a little zingier. still showed 60-point-something MPG this morning.

    I generally like to go by what the manual says - I figure the folks who designed the car should know what is best. Even moreso in this case.

    I'm disappointed that the guys who mount and balance tires routinely don't seem to put the right amount of air in them. Had a tire put on my Ranger and they put 40PSI in it. Calls for 30. The Ford Ranger is not known for a great ride - and it will literally bounce right off the road with tires that hard.
     
    #9 Valiant V, May 7, 2021
    Last edited: May 7, 2021
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  10. Mendel Leisk

    Mendel Leisk Senior Member

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    In the drivers door frame there’s a decal with the Toyota recommended air pressures. They recommend the rears a pound or two less than the fronts.

    What I do is set all four to the higher value. Less hassle, and I think the diff is trivial.
     
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  11. dolj

    dolj Senior Member

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    I use the factory recommended 240 kPa F/230 kPa R (35 PSi F/33 PSI R) on mine. From experimentation I found going higher gives marginally better MPG but at the expense of throwing the tires out prematurely due to waering out on the centers. Allowing the tires to go lower than placarded definitely gets worse MPG very quickly so it pay to be vigilent. YMMV.

    Given this is a Prius Gen 2 forum, it is pretty irrelevant what the pressures are for a 2017 Gen 4. Please be mindful of which forum you are reading and post accordingly.
     
  12. GabrielD

    GabrielD Member

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    I think the tire manufacturer would know better what pressure their tire should be at then the car manufacturer. Do I listen to what Toyota thinks I should put in these tires? I don't think so.. Follow what your tires say, not the door, unless it's as mentioned, the factory tires are exact replacements. Only down side is your TPS will think your tires are low as there's a set parameter for low readings.
     
  13. fuzzy1

    fuzzy1 Senior Member

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    I'd like to figure out why a small number of drivers have found this center tire wear, while large numbers don't experience it. Do certain tire models (or markets) have significantly different construction?

    Only steel belted radial tires are of interest here. Old fashioned bias ply tires are known to wear in this manner when overinflated, but I'm not aware that anyone uses such tires on modern cars.

    Tire and car makers have different interests here. Tire makers declare what is needed to operate the tires to their full load ratings and other specifications. Car makers want riders to have a comfortable ride, among other things. So these different parties may pick different balance points on the various tradeoffs.

    Then we have incidents such as the 1990's Ford Explorer / Firestone Fiasco, where tire failures lead to hundreds of fatal rollovers. Firestone received the initial blame, for leaving out one of the specified and necessary components. But Ford turned out to have plenty of blame too, for selecting a too-small tire, specifying a too-low inflation pressure, and having a suspension design prone to roll-over. And all these were exacerbated by customers ignoring tire pressures, vehicle load ratings, and speed limits.
     
    #13 fuzzy1, May 8, 2021
    Last edited: May 8, 2021
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  14. Ozark Man

    Ozark Man Member

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    I run 36 psi on my 2017 which is about 10 % over the recommended I think. I have always did this with whatever vehicle and the ride is ok and the tires always seem to last longer than expected.
     
  15. Valiant V

    Valiant V New Member

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    A thousand pardons! Newbie mistake.

    I'll be careful not to play in the wrong sandbox going forward!
     
  16. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Or just buy a Prius of each generation so you are never wrong! <G>
     
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  17. dolj

    dolj Senior Member

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    More than likely only a small percentage of drivers would go to the bother of actually measuring the tires using a method that would highlight the depth at the edges and centers.
    Correct, only talking about steel-belted radial tires. In this day and age who would use anything other than that on a Prius or any modern vehicle, for that matter.
    Most people change their tires before they reach minimums and unless they actually look at the tires closely they wouldn't even notice the uneven wear. The more depth overall the harder it is to see the difference. To document my experiment with different pressures, I measured the tires 6-monthly across the width at both edges and in the centers. It is pretty evident when you go to this effort.
     
  18. fuzzy1

    fuzzy1 Senior Member

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    I believe many users of above-placard pressures, both here on PC and over on CleanMPG.com (back when I was regular there) would dispute this. Or at least, any excess center wear from higher pressure accumulates much slower than the edge wear from low pressures.

    On my last two 20th Century cars, the tires did wear as if underinflated, until I boosted the pressure well above the door placard.

    Here in the U.S., lots of people wear down to minimums (2/32" in most states, 1/32" in certain drier southern states), or to where they become unhappy with wet traction (commonly near 4/32").

    =========================================

    P.S. Just now, checking a couple of the 'summer' tires on my 2012 Prius, Michelin Defenders run their entire life in the 38 to 44 psi range, I'm finding the two outer grooves (inside and outside) have 5/32nds inch of tread, or a hair more, depending on which tire and which measurement. The two center grooves have slightly deeper tread, 6/32nds inch or just barely under. The average difference is about 3/4ths of 1/32nd-inch. I.e. the center tread has not become thinner than the outer tread.

    Are you saying that the difference between inner and outer grooves was even greater when the tires were new? Or have I effectively been running them underinflated? Or do I have an undetected alignment problem that is causing a slight bit of excess wear on both edges, exceeding the over-inflation-center-wear issue you expect?

    This is why I'm wondering it there is some significant difference between the tires in your national market, and the tires I have been using.
     
    #18 fuzzy1, May 10, 2021
    Last edited: May 10, 2021
  19. dolj

    dolj Senior Member

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    That is an interesting thought but not one I have personally seen here. Maybe they do that in the States.
    Without a doubt, tires for NZ and Australia are specifically formulated for our geography, road type, and seasons. Generally, A/S tires are used and the range provided by each manufacturer is smaller as well as the actual manufacturers are fewer. We have other tires imported from the likes of Japan and Korea.

    You cannot generally get the same 'models' of tires here that I see mentioned in the US. E. g. the last time I bought Bridgestones the only Bridgestone Ecopia available here was the Ecopia PZ-X. Looking right now, I see now there are PZ-X, EP300, EP500, EP150, and EP25 but only the EP300 is available in the size for the Prius. Even if the model was the same I doubt the actual tire would be the same as the one sold in the US.

    In the end, the correct pressure (all else being equal) is the one where you have even wear across the whole width of the tread. Unfortunately, one size does not fit all and without taking that into account the debate will go on and on.
     
  20. Mendel Leisk

    Mendel Leisk Senior Member

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    Rear camber typically splays the wheels out at the bottom. Accordingly tire tread tends to wear faster on inner edges, regardless of tire pressure.
     
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