Nw LRR tires but they set to 35 psi?

Discussion in 'Gen 3 Prius Main Forum' started by Jim Caldwell, Sep 14, 2019.

  1. Jim Caldwell

    Jim Caldwell Junior Member

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    Just bought a new set of Michelin energy saver A/S tires for my 2010 prius. I asked what pressure they are set to and they said 35 psi. Well i asked if they were made to run at 44 psi as they are special LRR tires. They said that's just the max. The tire pressure on door pillar says 35, and thats what they go by. I thought that to get the low rolling resistance they had to run at a higher pressure than standard. Can i increase pressure to get better mileage?
     
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Lots of tire shops set the pressure to the value on the door sticker for liability reasons.

    You always have the option of deliberately over-inflating, and you will almost certainly get better MPG at the cost of accelerated tire wear and reduced traction… so choose your path carefully.

    You need to validate the results- add a little air, make sure the MPG really is going up as you add pressure, and periodically check the tire for an overinflation wear pattern. Everyone finds a happy medium.
     
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  3. Jim Caldwell

    Jim Caldwell Junior Member

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    I suspect some Prius motorhead in this forum has already done the experimenting with the Michelin Energy Saver A/S tires and found the sweet spot where mileage is increased the most, but ride and wear are still good. By the time....thousands of miles....i see that i have the pressure too high and the tires are worn in the center of tread.....well, the damage is done. What i was thinking is that at 35 psi, maybe the gas mileage is NO better than a non -LRR tire?
     
  4. bisco

    bisco cookie crumbler

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    LRR vs non LRR has nothing to do with pressure, and everything to do with tread and rubber.

    no one has done testing of different pressures effect on mpg's.

    many believe anecdotally that higher pressures increase mpg's, and there is no evidence to the contrary.

    as you raise pressure above the factory recommendation, which should be 35f/33r i think? you will get a stiffer ride and probably more suspension wear.

    i run mine at 42/40, but i have a little ocd
     
  5. Pdaddy

    Pdaddy Junior Member

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    Try calling Michelin and see what they recommend. Tire pressure should also be measured cold prior to driving which does not happen when going in for a rotation.

    SM-G960U ?
     
  6. sam spade 2

    sam spade 2 Senior Member

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    Maybe but don't get carried away.....because having too much air causes some other bad things to happen.

    For instance, harsh noisy ride, extra wear on suspension components, uneven tire wear and reduced traction.

    It is likely that the original tires were LRR too and the recommended pressure took that into consideration.

    IF you just MUST do this to up to 39 or 40 and see how you like it.
    The 44 on the sidewall is NOT intended for a vehicle as light as a Prius.
     
  7. Grit

    Grit Senior Member

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    44psi on all 4s on mine for years, all wears evenly since tires were new.
     
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  8. jb in NE

    jb in NE Senior Member

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    I would bet that in the long history of automobiles and tires, somebody has done such a test.

    Edit - here is just one example:

    They are going to recommend the manufacturer's setpoints on the door pillar. They didn't design the car on which the tires are installed, and aren't likely to recommend something different that could cause them liability issues.
     

    Attached Files:

    #8 jb in NE, Sep 14, 2019
    Last edited: Sep 14, 2019
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  9. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    What they're saying is spot-on.

    No.

    Marginally better, but I would be cautious, and definitely would not run them at max sidewall. The ride will be harsh, cornering traction may suffer, and I suspect steadily running tires at much higher than specified (in the sticker on door pillar) is going to be hard on the the wheel bearings and suspension, accelerate wear-and-tear.

    If it was Costco, for one, they will flat-out refuse to pressure higher than spec. Nothing's stopping you raising the pressures yourself though. Still, my 2 cents: stick with spec, or at most 2~3 psi more.
     
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  10. sam spade 2

    sam spade 2 Senior Member

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    Well of course, somebody will always chime in with "I've done that for years and had no ill effects."
    That does ***NOT*** mean that it is a good thing for everybody to do.
     
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  11. ASRDogman

    ASRDogman Senior Member

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    Just because you can do something, doesn't mean you should, or that it's safe.
    Higher pressure could mean higher temp's. Handle will be different.
    Just because one person doesn't get hurt, doesn't mean someone else won't.
    And it doesn't matter that some innocent person won't be injured because of someones neglect.

    They recommend a certain pressure for a reason. They don't do just to ruin your fun. :)
    Any tire can only take X amount of pressure befor it becomes dangerous.
     
  12. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Think I read lower pressures will run hotter, more flex. But yeah, I would still stick near the spec'd pressure, the sweet-spot.

    The Energy Saver A/S's should deliver good mpg at that pressure, compared to other tires at same pressure.
     
  13. ASRDogman

    ASRDogman Senior Member

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    Too low or too high will cause heat.
    The average passenger tire will see more tire wear on the outer edges if the tire is low.
    The middle if they are over inflated.
    Some hi performance tires will do the opposite because the outer edges are harder rubber to last
    longer for the harder cornering.
     
    #13 ASRDogman, Sep 14, 2019
    Last edited: Sep 14, 2019
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  14. bisco

    bisco cookie crumbler

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    the max sidewall pressure is usually your max, with a safety margin of error thrown in on top.

    speed, ambient temp and gross vehicle weight are part of your consideration as well.
     
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  15. Robert Holt

    Robert Holt Senior Member

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    That PDF was a fascinating read! The critical info for me was Table 3 of inflation pressures versus expected fuel savings. As best I can make out, Table 3 was based on a computer model rather than on observed data. Given the age of the report, I expect that it was designed to predict fuel savings on biased-ply tires as radial tires were quite new then. Furthermore, we Prius owners seem to be in a different area on the graph as their base tire pressure was 24psi whereas we are discussing raising the Prius base tire pressure from 35 psi to 40 psi or so, which would be higher pressure ranges than the predictions of Table 3 encompass. The predicted fuel savings might still apply in our case, but given all the caveats that is not a slam-dunk conclusion. Real observable data that randomly changed cold inflation pressures on cars in consistent test conditions from 35 to 40-42 would be valuable.
    +1 anecdotally: when driving home from the first three dealer services, I was astonished to see the MFD fuel consumption on our 2012 Prius drop from mid-50s to 50mpg or so, a noticeable decrease. I finally found out that the dealer had reduced the 40-42 psi tire pressures to 35 psi, and as soon as I pumped them back up to 40-42, the mpg returned to the mid-50s.
     
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  16. bisco

    bisco cookie crumbler

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    real world data would be invaluable, and you might not need it on every tire model.

    maybe then, i could reduce my pressures to the door jamb without worry
     
  17. Grit

    Grit Senior Member

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    I don't recall in my previous post suggesting the OP to follow suit :whistle:
     
  18. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Still, I'm leery, thinking about increased wheel bearing and suspension stress. I typically keep all four at the same pressure, just a pound or two over spec.

    Another factor, I've got 3 go-to gauges, and they all read different. Maybe food for thought.
     
  19. Grit

    Grit Senior Member

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    You got bad tires then, go visit your local dealership :ROFLMAO:

    My JNCAIR air compressor gauge, racing psi reader and techstream are typically -/+ 2psi from each other, sand pound.
     
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  20. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Huh? Near-new Michelin Primacy mxm4. 215/45R17, which tend to ride harder than 15", but quite smooth. Reminds me though: the weather's getting cooler; I should maybe bump them up a pound or two.

    Bottom line for me though: any tire is going to be less resilient at higher pressure, transmit more shock through to the wheel bearings and suspension. It's a trade-off, but I'm ok with a little less mpg.

    Yeah I've got 2~3 pounds spread, between a cheapy digital and couple of (good quality) stick gauges.
     
    #20 Mendel Leisk, Sep 14, 2019
    Last edited: Sep 14, 2019
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