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    MoMoPrius New Member

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    HI,

    I just installed some Michelin Radial X tires from SAM's. In all my cars, I run 32psi since 44psi is max on the sidewall. I hear peeps running 44psi or more...what's the deal???
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    fuzzy1 Senior Member

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    Location:
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    Your Vehicle Year:
    2012 Prius
    Model:
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    For your model / tire size, the door placard recommends 35 front, 33 rear, and conventional wisdom here on PriusChat says to not go any lower. Older models were notorious for chewing up tires too quickly at recommended pressure, and higher pressure helped tread longevity. I don't recall many similar complaints about this generation, but it seems that few of us run at just the placard pressure.

    Higher pressure than placard also helps mpg, at the expense of ride harshness. "Ideal" pressure is thus a tradeoff, and a very personal choice.
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    tumbleweed Senior Member

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    I agree with Fuzzy, it's your choice. But the pressure recommended on the door post and in the owner's manual should be the minimum, measured cold, that you ever use. The pressure on the sidewall is the pressure for maximum load and most of us do not exceed that pressure.

    Higher pressures, within reason, will give you better mileage, better resistance to hydroplaning, and better handling under most conditions. Lower pressures give a better ride. I have not noticed any difference in tire wear from higher pressures, even with 44psi the tires should still wear even across the tread.

    You could raise the pressures up to 38 or 40 and give it a try, see what difference it makes to the gas mileage. If you don't like the harsher ride lower them back down.
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    F8L Protecting Habitat & AG Lands

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    There have been many tests showing that tires that are inflated with higher pressures roll easier and further. Thus many of us run well over 40psi. My max pressure is 44psi on my 15" tires. I run 45/43 or even higher in the summer. My 17s are rated 51psi max and for comfort I keep them at 45/43.

    Pros:

    • Better mpg
    • Better handling in corners
    • Better tire wear
    • More even tire wear
    • Improved hydroplane resistance
    Cons:

    • Harsher ride
    • More tire noise
    • Constantly fighting with the dealership or tire places to keep your pressure above placard levels. :)
    • Can make the car seem "twitchy" at high speeds
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    xpcman Active Member

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    I find that the Michelin Radial X tires are rather twitchy at high speeds when run at higher pressures. I run 38 front/36 rear on the wife's 2008 and find that's the best balance.
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    hill High Fiber Member

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    Funny you should mention a psi in the 50's ..... because I've heard this one moderator mention a pressure that I now use comfortably ......
    but of course I'd NEVER recommend that anyone do what I do ....

    :eyebrows:
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    djlen Junior Member

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    Can someone define "twitchy" please. :)
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    F8L Protecting Habitat & AG Lands

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    The car wanders more and steering input is faster so the car feels twitchy. The car starts to wander so you correct with the steering wheel and the car quickly responds. In some cases this can happen enough that the car feels like it needs epilepsy meds. It's really not that bad but can be annoying.
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    tumbleweed Senior Member

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    I think what we call "twitchy" is caused by poor tracking. A good quick test is how long will your car go down a flat straight section of highway without needing a steering correction to stay in your lane. If you can relax while driving and not have to make constant steering corrections to stay in the center of your lane the tracking is OK.

    My Gen2 Prius was very twitchy due to alignment problems with the rear wheels, I think it was damaged in shipment. I finally fixed it by shimming the rear wheels to correct the toe. That helped and made it more or less drivable but it was never as good as I would have liked.

    My Gen3 Prius is just the opposite, it is the most stable car I have owned since my old Honda Prelude. I can normally go down the highway for at least 15 seconds without a steering correction (LKA off) if I get it pointed correctly, assuming no wind, and a good section of highway. Unlike F8L I can detect no difference in tracking with changes in tire pressure, I have used various pressures from recommended to 51 psi with 3 different kinds of tires and it's always good in that respect.

    BTW I now have about 2500 miles on my Michelin Primacy MXM4 tires, I have raised the pressures from recommended to 40psi at 40 degrees. Car still drives great, difference in ride is barely noticeable, and mileage seems to have gone up at least 5% over recommended pressures.
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    F8L Protecting Habitat & AG Lands

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    Along the lines of Tumbleweed's post I should state that my rear alignment is just within spec but just barely. This could be why I notice more twitch. Could also be because I still drive a GenII. :)

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