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Do you really need more air pressure in front?

Discussion in 'Gen 2 Prius Main Forum' started by Ironworks, Apr 11, 2005.

  1. Ironworks

    Ironworks New Member

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    I have never had a vehicle that required more or less pressure in particular tires. My prius not being perfectly balanced is not a new development, most vehicles are not.

    Why the difference?

    I stopped at a gas station to increase the pressure in my tires to 42F/40R and found out that they were already there. (from 38/36)

    Excluding the warmer weather, how much pressure do your tires gain while driving?

    Does nitrogen expand less due to driving or warmer weather?

    Thanks
     
    #1 Ironworks, Apr 11, 2005
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    The Prius is quite front-end heavy. ~60% of the weight is towards the front. For any car, increasing the front tyre pressure by 1 or 2 PSI will slightly improve handling and perhaps that's what Toyota wants to do here. (The Camry we havehas the front tyres 2psi higher than the rears even before we bought the Prius). Also the pressure is needed to support the weight.
     
    #2 Tideland Prius, Apr 12, 2005
  3. Ironworks

    Ironworks New Member

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    I would think most cars are carrying 60%+ of the weight in front due to the engine. This is just my first vehicle that has recommended this. You would think that all manufacturers would do the same.
     
    #3 Ironworks, Apr 13, 2005
  4. gaulfinger

    gaulfinger New Member

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    It it's not an absolute: more pressure = more handling.

    Increasing pressure in front relative to back (either by adding to the front of subtracting from the back) will change handling characteristics away from understeer towards oversteer.

    Understeer is the tendency of the front end to "plow" into a corner. Oversteer is the tendency of the rear end to swing out in a corner. The latter is considered very dangerous--it's easy to lose control of the car.

    Most cars are tuned for moderate to heavy understeer because it's less likely to surprise someone by going tail-first into the trees. A neutral car, like a RWD BMW or Corvette or something, is tuned to be close to "neutral" for a more balanced feel. Hi performance cars like a Porsche 911 are notorious for needing expert driving skills to keep the rear end in line. The reward is superior overall cornering capability and feel. But for most people, eeking out that little extra thrill isn't worth the risk plucking said trees from the rear bumper...

    A car like the Prius might get a slight improvement in feel from increasing the front pressure, and maybe slightly higher limits. I doubt there could be such a swing towards oversteer from pressure change to put it in any risk.

    But I think most people are talking about adding air to get a harder riding tire for the sake of fuel economy... Staying within the constraints of load, wear, ride, and economy, I don't think anyone is going to come up with such a spread between front and rear pressure to put the car in danger of oversteering.

    That said, experimenting with pressure is a good way to fine tune to your own preferences in feel, ride, economy, etc.

    Gary
     
    #4 gaulfinger, Apr 16, 2005
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