never over inflating my tires again

Discussion in 'Gen 2 Prius Fuel Economy' started by oil_burner, Apr 3, 2019.

  1. alanclarkeau

    alanclarkeau Senior Member

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    I've had quite a few cars with higher REAR pressures than FRONT. FORD Focus: 31 FR, 33 Rear, unless fully laden, then 35 FR, 41 Rear.

    My 1977 Renault had something like 23 front, 27 rear - and I had an "incident" when they were rotated, but they forgot to swap the pressures - it oversteered wildly. My VW Microbuses not only had higher rear pressures, but slightly wider tyres.

    That's why I was surprised that PRIUS (Gen 4) had lower Rear than Front pressures - maybe because it's balanced well with a heavy battery pack over the rear axle.
     
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  2. fuzzy1

    fuzzy1 Senior Member

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    I should note that North American tire pressure recommendations don't necessarily match Rest-of-World labeling. After reading here that some models in Europe have labels recommending increased rear pressures when heavily loaded, I personally verified such on a couple rental cars over there. (Photos deeply buried somewhere in my unlabeled vacation archives, not yet extracted for this forum.) IIRC, one car displayed 2 load-dependent choices, the next 3 choices.

    That sort of multiple-choice pressure recommendation is essentially unheard of here. Our physics isn't any different, so it must something about our market (customer preferences? marketing? legal climate? too complex for our drivers?) This is yet another reason I don't take our label recommendations as gospel.
     
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  3. ALS

    ALS Active Member

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    Agree fuzzy1, my RWD 97 Volvo the door sticker says 36 psi all around and it drives OK. Pump the tires up to say 42-44 and I have my hands full in the rain. The steering is what I would call twitchy or overly responsive. I settled at 40 psi, the car is close to perfect with the handling and ride.

    I'm with you on the door sticker recommendation, it makes a good starting point to play with the pressures to find that sweet spot.
     
  4. Zeppo Shanski

    Zeppo Shanski Member

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    Can someone please explain the theory/strategy behind the front/rear inflation difference please.




    TIA for your response.
     
    #64 Zeppo Shanski, Apr 8, 2019
    Last edited: Apr 8, 2019
  5. Robert Holt

    Robert Holt Senior Member

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    Wheel Alignment, or more accurately lack of correct alignment, can also dramatically affect tread wear in my experience with other vehicles. Our Prius with Michelin Energy Saver A/S tires has even treadwear across the tread after 50,000 miles, but I also had a 4-wheel alignment performed shortly after I had them installed.
     
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  6. hill

    hill High Fiber Member

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    riddle me this - after Google'ing how high the pressures are on NASCAR, Formula 1, etc .... why is it your street tires don't benefit more - from measly 36lbs?
    Or ... maybe ask oneself, why is it your typical average White Freightliner or Peterbilt will run 110 PSI in their front tires? And yet (never mind their heavier liads for now) they don't experience wacky treadwear in the center?
    do or don't do whatever you want. I run my tires up near 50 lb & I've gotten over 90,000 miles with one particular set of Michelins, prior to selling the car, with plenty of (nice - even) tread still left on them. Over 20k miles on another set of Michelin and you'd be hard-pressed to even notice if they are worn. In short, there are other things that can affect how tires wear, besides tire pressures. The old wives tale about bald equals overinflation was definitely true back in the day of bias tires. Not trying to convince anyone. Just sayin' .....
    the manufacturer knows what side of the bread that the butter is on. So if you can get a nice smooth ride at 36 PSI, that's what they'llrecommend, despite getting much worse hydroplaning Dynamics in rainy conditions. There is always a maximum rating of a tire, & take a look, it's definitely way above 36 PSI. Under-inflation? That's an entirely different animal. Do not do that - unless you are out on the sand dunes. In that case, drop them down to 5 to 7 lb to prevent getting stuck way too easily. Then re-inflate ASAP.
    Disclaimer ;This experience as well as the OP's experience are both anecdotal.
    .
     
    #66 hill, Apr 8, 2019
    Last edited: Apr 8, 2019
  7. davran

    davran Junior Member

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    The pressure listed on the door tag is always for comfort -- I find it feels floppy. On every car I've owned I've run 36-38psi, with no abnormal wear.
    My '05 vw passat tdi wagon listed 38psi front, and 42psi rear on the door jamb.
     
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  8. hill

    hill High Fiber Member

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    Yep.
    Here's our Model X readout ;
    20180315_132443.jpg

    and here's our (turo) plugin minivan while ours was in the shop;
    20190311_180157_HDR-1.jpg

    practicing what we preach

    .
     
    #68 hill, Apr 8, 2019
    Last edited: Apr 8, 2019
  9. alanclarkeau

    alanclarkeau Senior Member

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    A higher pressure can increase grip to an extent. So they balance oversteer/understeer. Anyone who had a VW Beetle (and I'm told PORSCHE) would bump up the rear pressures to balance it out. Or - put better quality tyres on the rear. By the 1980s, the PORSCHE 911 had bigger wheels and tyres on the rear (as do most similar cars - the Lamborghini Countach in early/mid '70s had wider back wheels).

    Probably not very relevant to a PRIUS, which has almost identical F/R tyre pressures.

    But it also can improve load carrying capacity - so sometimes wagons and vans can have higher rear pressures. My Mazda 929 Wagon had 26 fr, 32 rear, but the sedan had 26 f/r.
     
  10. Zeppo Shanski

    Zeppo Shanski Member

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    THANK YOU.


    It's funny. When I was a snotty punk w/ hot-rod cars we played with tire sizes but not so much air pressure. It's funny too that we only looked at 1 number. ... My Charger had 50's on the back and 70's on the front. My Talladega had 60's all around.
     
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  11. alanclarkeau

    alanclarkeau Senior Member

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    Found this - it was hiding yesterday. Note that this is for performance cars - more on the track, I suspect - but the principle is the same. Or if you're into hanging the rear end out on gravel roads ... .

    upload_2019-4-10_13-4-32.png
     
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  12. Zeppo Shanski

    Zeppo Shanski Member

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    LOL.

    Those days are past me ... or am I past those days? I don't have any inclination to drive my Prius the way I drove my muscle cars. I do however appreciate your interest in helping me out.

    Both my Charger and Talladega got mileage registered in GPM ... gallons per mile; at least it seamed that way.
     
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  13. alanclarkeau

    alanclarkeau Senior Member

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    Never had a muscle car - but even gutless old RWD cars were fun on bush tracks - if I didn't have a passenger.
     
  14. ALS

    ALS Active Member

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    And don't you wish you still had that Talladega buried under a tarp in your garage?
     
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  15. Zeppo Shanski

    Zeppo Shanski Member

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    20/20 hindsite is crystal clear. ... Shouldda, couldda, wouldda and $1.80 gets me a coffee at the Speedway.

    The Talladega was flat out as cool a car as ever made ... but $70,000 is about as good as you're gonna get for one.
     
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  16. alanclarkeau

    alanclarkeau Senior Member

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    Just looked it up - never heard of them, looks like fun.

    As for cars - if I go through my list of cars I'd owned on the basis of "if I still had it today" - only 2 stand out. 2 VW Microbuses, a 74 Manual and a 77 Auto with Air-Conditioning. Both were immaculate when I sold them. They're the only ones which are worth vaguely serious money today. Who'd have thought.
     
  17. George W

    George W Active Member

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    Aren't the front tires supposed to "toe-in" slightly? When was the last time the OP had an alignment?
     
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  18. hill

    hill High Fiber Member

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    don't fret it ... if VW follows through with their threat, there is an all electric Microbus on the way. I don't know how well it would be - but it really sounds cool. There are several pictures online & it looks really nice.
    .
     
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  19. alanclarkeau

    alanclarkeau Senior Member

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    Yeah - the first concept came out - what feels like a decade ago, then the electric concept.

    My A/C one had a massive condenser with 4 fans sitting under the middle of the body - it did cross my mind that one of those old Microbuses (or campervan) would be a good project to convert to electric - pack the batteries underneath. But I think they should be weatherproof - so that complication could be the killer of that idea.
     
  20. oil_burner

    oil_burner Active Member

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    Well your question is leading. And it is entirely based on the wrong idea of "let's ignore the load" which is half the design equation of the tire. To answer your question truck tires have way more plies and are designed to carry heavy loads at high psi and not overheat. Race car tires are designed for ultimate grip and have rubber that isn't fully vulcanized until they get up to race temperatures where they provide the most grip. Neither have anything in common with a Prius hypermiller running 50 psi to save gas.
     
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