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do you get better mpg's if you over inflate the tires?

Discussion in 'Gen II Prius Main Forum' started by ski.dive, Mar 25, 2012.

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  1. ski.dive

    ski.dive Member

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    I heard some people over inflate their tires for better gas mileage.

    Any proof?

    Is this true or just B.S.?
  2. bisco

    bisco cookie crumbler

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    it seems to be hit or miss. i have tried it without success, but others swear by it. i don't think there have been any controlled experiments. i keep mine a few over so i don't have to check them too often.
  3. F8L

    F8L Protecting Habitat & AG Lands

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    The only good experiments that I have seen were based on rolling distance in a coast down test. The higher the pressure the further the tire rolled before it came to a stop. The further a tire will roll with the same energy input the better mpg will be in most circumstances. Some road surface types could alter this.

    Mythbusters gave these results from their test:

    Control, 35psi (manufacturer recomendation)
    tyres at 10psi = 3.7% increase in consumption
    tyres at 30psi = 1.2% increase in consumption
    tyres at 40psi = 6.2% decrease in consumption
    tyres at 60psi = 7.6% decrease in consumption

    MythBusters: Tire Pressure Test : Video : Discovery Channel

    Here is the test done at Ecomodder.com
    Experiment: coast down distances (rolling resistance) @ various tire pressures - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

    PSI/Distance in feet

    20 / 479.3
    25 / 524.8
    30 / 621.0
    35 / 621.0
    40 / 639.6
    45 / 687.5
    50 / 702.0
    55 / 699.3
    60 / 702.0
  4. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Over inflating your tyres does give an increase in mpg's BUT can cause other issues depending on your jurisdiction. It can cause poor handling, increased braking in the wet, poor cornering etc, which could invalidate your insurance if it was found this caused an accident. That then opens you up to all sorts of issues. If you know the risks, then on your head be it, otherwise just keep the car psi's at the correct level and no more but certainly no less.

    I personally keep mine on the correct psi or just 1 psi over and get some good mpg's.
  5. jdenenberg

    jdenenberg EE Professor

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    Never "over inflate" tires (defined as more psi cold than the max rating of your tires). The psi suggested by Toyota will not give the best performance as different tire/brand models as each will do best at different pressures. The 35/33 setting that Toyota suggests is optimized for a comfortable ride not MPG, handling, or traction.

    I buy tires that have a max rating of 51 psi (Nokian WRg2) and find that 42/40 seems to be a good compromise for my use. Yes, that does result in improved MPG and handling with no noticeable effect on traction.

    JeffD
  6. ursle

    ursle Gas miser

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    It would be silly to over inflate your tires, as a matter of fact I hear you get much better traction by running them at 10-12psi, but that it's even safer to fill them with calcium chloride, never go flat, ride over anything, etc.
    Personally I inflate to 40 all around with nitrogen, the sidewall marking for highest pressure is 1/2 the bursting pressure...
  7. hobba

    hobba New Member

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    I've tried it as well and for a long period of time. Never found that the MPG's increased for me. Blew thru a set of Yokohama A530's in 23,000 miles. Just replaced them two weeks ago. I'm going to run normal pressure from now on. That was my experience at least.
  8. MJFrog

    MJFrog Active Member

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    What was the treadwear pattern? Even, all the way across; outer edges worn; center tread worn?
  9. uart

    uart Senior Member

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    Font wars. L O L
  10. uart

    uart Senior Member

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    And now for a serious reply. Yes I think I get slightly better MPG and handling at 42/40 psi.

    Actually I was quite surprised when I recently bought new tires to find that the tire shop had already inflated the new tires to 42 psi and recommended that for best handling and wear.
  11. nh7o

    nh7o Off grid since 1980

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    I got my Prius with Michelin LRR tires, which were initially inflated to only ~32 psi. I increased to ~44 psi, the side wall rating, after reading reports here on PC. I noticed a few mpg's improvement on level, high speed sections. On the slower, very hilly areas, not much difference.
  12. hobba

    hobba New Member

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    Tread wear pattern was even across the tires. Tread wear indicators were displayed and the sidewalls showed evidence of early cracking. The tires were rated for 60K miles, so I got a proration from the dealer. I was very religious in monitoring the tire pressures and keeping them inflated as I have my own air pressure tank. But it just didn't work for me at least.
  13. MJFrog

    MJFrog Active Member

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    Bummer... Even tread wear indicates they were run within pressure tolerances...neither too low, nor too high PSI. Tough that they didn't last as long as they should have.
  14. uart

    uart Senior Member

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    Then don't blame the higher pressure for the short life then. Running at a lower pressure would probably have resulted in even lower tread life (as you would probably have had more wear near the edges).
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