Now I think I know why my mpg has been so good

Discussion in 'Gen 4 Prius Main Forum' started by jbkendrick, Jul 2, 2016.

  1. jbkendrick

    jbkendrick Active Member

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    Embarrassed to say this, but I've had my car for two weeks and 1,200 miles and I just checked my tire pressure for the first time this afternoon. And the dealer had 50 lbs in all four of them. Placard said to have them at 36 front and 35 rear, so I lowered to 40 in all tires. I always ran my Insight tires a bit high and it did help mpg, but I think 50 is just too high. It will be interesting to see the change in mpg. J
     
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  2. sttkailua

    sttkailua Active Member

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    jbkendrick,

    I recall seeing another post on high tire pressure.
    Reason was that they inflate it high from the factory, and
    the dealer is supposed to lower it to recommend pressure
    before the sale. Sometimes they forget to do this.

    With summer heat here, it is dangerous if tire pressure gets too high.
    What kinda mpg did you get?

    stt
     
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  3. bisco

    bisco cookie crumbler

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    did the ride feel too hard? if not, i think i'd leave them at 50, unless that's above the max sidewall rating. mine are 42/40.
     
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  4. Coast Cruiser

    Coast Cruiser Senior Member

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    Kevin was kind and told me the Max PSI for my 15" Toyo tires is 41. (My crummy eyes couldn't see it.)
    The door placard recommends 36/35. But I set all four tires at 40, and the ride is still smooth. There seems to be no negative affects in cornering or overall handling.

    Did the 40 PSI improve the gas mileage? The jury is still out. It jumped up 2 or 3 mpg for awhile (to 63) but as the tank emptied I started seeing the normal 60 mpg that I always get. Either way, 36 or 40 is good. I don't think I will concern myself too much with the tire pressure.
     
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  5. fuzzy1

    fuzzy1 Senior Member

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    Based on past discussions, I very much doubt that the factory shipping pressure will lead to dangerously high pressure in the summer heat. But your rump may not appreciate the harsh ride.

    What max pressure rating is molded into the sidewall? 44 or 51? Remember, that is a cold pressure rating. We can't expect drivers to release some pressure every hot afternoon, so the tires must have enough margin to handle it. Numerous hardcore hypermilers, who tend to not apply other overstresses to tires (high speeds, heavy loads, etc.) go above that.
     
    #5 fuzzy1, Jul 3, 2016
    Last edited: Jul 3, 2016
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  6. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    Makes you wonder what else the dealership missed. Maybe check the spare tire pressure.

    Did you get a "how'd we do" opportunity from the dealership? Maybe let em know. As high up the chain as possible.

    There could other items missed. I believe there's locating pin holes on the underside that the dealership is supposed to put plugs on, for example.
     
  7. Redpoint5

    Redpoint5 Senior Member

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    50 PSI isn't a safety concern, but more of a ride comfort thing. I'd run 'em as high as you can tolerate the ride, up to about 50 PSI. Burst pressure is something like several hundred PSI; well above what typical compressors are able to put out.

    The MPG difference between 40 and 50 PSI won't be as great as comparing between 30 and 40 PSI. There are diminishing returns the harder you go.

    Note that spare tires almost always have a higher PSI rating, and require more pressure since the contact patch is much smaller.
     
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  8. ETP

    ETP 2019Prius(Limited),Highlander HYB Plat,B52-D,G,F,H

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    Ran my Hondas at 51PSI but could not do that on a Prius. Front end would skip hitting holes in the road.
    40-42 is the sweet spot. Cold check only. Do not check your tires hot unless it is an emergency.

    BTW, had a 2008 Corolla that I bought in Guam in 2008 and it had 90PSI in the tires.
     
    #8 ETP, Jul 3, 2016
    Last edited by a moderator: Jul 4, 2016
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  9. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    Having the low profile 17" tires I stay pretty close to the spec'd. 33/32 psi (front/rear); I keep them around 36 all around. Higher runs too harsh for my taste, and doesn't seem to improve rolling resistance, at least not enough to notice.
     
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  10. jbkendrick

    jbkendrick Active Member

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    I've been getting consistent mod 60's, and drive mostly highway and suburban roads, about 10
    Thanks ETP. Sidewall indicates 44psi as Max, so I think I'll try 40 for a while and if mpg decreases too much take it to 44.
     
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  11. jbkendrick

    jbkendrick Active Member

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    Not sure about the ride except it was perhaps a bit smoother than my Golf. My expectations were not high so perhaps I'll notice a smoother ride now that I've decreased by 10psi. Also this is cold tire pressure as my car had been sitting for almost 24 hours before I checked them and it was about 75 degrees f at the time. J
     
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  12. David Beale

    David Beale Senior Member

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    Well, I suspect you are incorrect about "burst pressure" being several hundred PSI. There WAS the posted picture of the Prius that had a tyre burst while on the lift at a dealership. It was stated the woman who owned it "kept putting air in the tyres because she was told to". ;) It was also stated there was 60-70 PSI in the other three tyres.

    As I recall, the bursting tyre blew off the fender. :)
     
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  13. Kenny94945

    Kenny94945 Active Member

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    Cost of tires vs cost of fuel.

    Higher pressure could (could) create excessive wear to the center of the tire.

    There is so much to pressure and operating temperatures.
    A pyrometer is a good, even necessary, tool to own.
    If free, nitrogen is also a good air upgrade.
    I like digital tires gauges that read in 1/2 pounds.
     
  14. bisco

    bisco cookie crumbler

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    i think the max on my goodyear assurance is 50. that's what i put them at when away for awhile.
     
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  15. bhtooefr

    bhtooefr Senior Member

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    Mine was just weird - the driver's front was at 55, the other three were at 35-36.

    I set everything at 40, and am happy with the ride quality and the resulting fuel economy, so...
     
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  16. ETP

    ETP 2019Prius(Limited),Highlander HYB Plat,B52-D,G,F,H

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    Ran 44 for years but finally gave in and did 42 after watching Hitch Hikers Guide to the Galaxy. (which is a Ford manual)
     
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  17. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    Sounds like the guy lowering pressures was on it, did three of them, then got pulled away, distracted.
     
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  18. Redpoint5

    Redpoint5 Senior Member

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    I suspect you are incorrect about me being incorrect about burst pressure :p

    Tire manufacturers don't publish burst pressures, but someone in the industry mentioned the burst pressure being "several hundred PSI". This article linked below has a quote from someone that worked for a major tire manufacturer, and he says;

    "A new, quality tire will not pop at an even multiple of the "max press." I'm sworn to secrecy about the exact burst pressure, but I wouldn't hesitate to double the "max press" of any new passenger-vehicle tire on a new wheel."

    I don't doubt that there have been tires that blew out at pressures below 100, but they were most likely damaged.

    Just look at your flimsy road bicycle tires. They can go to 110 PSI safely, and they are extremely thin compared to a passenger tire.

    6 Common Tire Myths Debunked
     
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  19. PriUncut

    PriUncut Active Member

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    Are most people running the same pressure all around?

    I just started running my 17's at 37 front, 35 rear and I've noticed the MPG improvement. But I'm just wondering if I should run the same pressure all around?
     
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  20. Redpoint5

    Redpoint5 Senior Member

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    I'm running something like 43 PSI front, and 41 PSI rear. The difference is due to the uneven weight bias of the vehicle. The engine is up front, so a higher percentage of the vehicles weight rides on the front tires.
     
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