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Tire Size

Discussion in 'Gen 2 Prius Main Forum' started by DanThePodGuy, Feb 26, 2005.

  1. DanThePodGuy

    DanThePodGuy New Member

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    Just before the Mercedes died and we put in our name for a Prius, we put new Michelin tires on. Sicne the car is shot and the tires new I want to transfer thm to the 2005 Prius. The only difference in tire size is 195 vs. the 185 on the Prius.

    I called the dealer and was told that changing the tire size would screw up all of the systems on the Prisu including the regenerative braking. Sicne the dealer said there was no way to turn off the beeping when in reverse, I am highly suspicious of anything they tell me.

    Any issues with 195 tires over 185.

    Thanks
     
    #1 DanThePodGuy, Feb 26, 2005
  2. ammiels

    ammiels New Member

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    I should defer to the Mavens like Jorgenson, but.
    The difference lies in the width of the tread. If the ratio is the same ie 65 then the height of the sidewall is different and therefore the rolling radius of the tire and therefore the circumference. If all 4 tires are replaced the only problem will be that any calculation that counts tire revolutions will be *somewhat* off. You will appear to be driving slower and less distance than actually. There are no safety issues involved. Your dealer lacks understanding. Peace, Ammiel
    If you wish to inform yourself on this subject click on the TireRack ad and go to upsizing
     
    #2 ammiels, Feb 26, 2005
  3. ggood

    ggood Senior Member

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    Plug-in Advanced
    I assume you're saying the Michelins are 195/65/15, in which case this tire size calculator says the speedometer would show 2.1% too slow: Miata Tire Size Calculator

    Navigation system has a tire calibration setting to adjust for new size tires, which solves the problem for the navigation. I assume this also causes the speedometer to show the correct speed. I'm not sure if the non-navigation cars have this setting.

    Because the tire is heavier and wider, you would see a minor reduction in fuel economy, but slightly more stability.

    Based soley on reading sites like this one for the last year and a half, I'd say the other dealer arguments are bogus.
     
    #3 ggood, Feb 26, 2005
  4. DanMan32

    DanMan32 Senior Member

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    No, that wouldn't solve the speedometer, or the MFD, or the odometer. The combination guage sends pulses which translates to wheel revolutions to the NAV and the MFD. The NAV compensates for the differential of distance based on revolution pulses based on GPS readings.
     
    #4 DanMan32, Feb 28, 2005
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