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I think I have weird sized / non-oem tires?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by moshbit, Mar 15, 2019.

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  1. moshbit

    moshbit Junior Member

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    hey folks, first post, although i've been lurking for a while. just picked up a 2008 base for 4k with 170k mileage on it. i realized today that i have studded snow tires and since the snow is melting, i need to get regular tires put on it. I've cruised through many of the tire threads here and have settled on the Michelin energy savers.

    problem is, i'm a little confused about what size to get. just about every site says my tires should be 185/65R15, but my current snow tires are P205/65R15 92T.

    should i buy the the 185/65R15 or the same size that's on my car currently?

    also, im not finding any of the 185's for the Michelin energy savers, just the 195's. is that close enough?
     
    #1 moshbit, Mar 15, 2019
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    185/65R15 is the correct size. If you use a wider tire, the diameter also will be larger which will introduce some speedometer and odometer error.
    Regarding the snow tires, I would have thought that a wider tire is not helpful with regards to improving traction on snow and ice.

    You can use 195/65R15, but 195/60R15 would be better with regards to maintaining the same tire diameter as the spec size.
     
    #2 Patrick Wong, Mar 15, 2019
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  3. edthefox5

    edthefox5 Senior Member

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    As long as the aspect ratio of 65% and the wheel height of 15 inches does not change going with a wider tire should not change speedometer reading.

    I run 205-65-15's on my car no problem.
     
    #3 edthefox5, Mar 16, 2019
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Whoever owned the car maybe picked up some used snow tires cheap. Yeah check in the Owner's Manual, and if it's missing you can download from Toyota Tech Info, and a few other Toyota sites I believe. Toyota Tech Info (manuals section) is always my go to.

    Page 468 of Owner's Manual:

    upload_2019-3-16_10-27-49.png
     
    #4 Mendel Leisk, Mar 16, 2019
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  5. moshbit

    moshbit Junior Member

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    Okay, that definitely helps. Thank you for the information!
     
    #5 moshbit, Mar 16, 2019
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Ray,

    You may not perceive a problem. However the speedometer/odometer reading is changed. The aspect ratio defines the relationship between tire width and tire sidewall height. This is unrelated to wheel diameter.

    185/65R15 has a circumference of 76.8" according to this tire size calculator. Tire Size Calculator
    205/65R15 has a circumference of 80", hence a difference of 4.2%. At a speed of 70 mph, this is an error of 3 mph low.

    195/60R15 has a circumference of 76", hence an error of 1% compared to the spec size tire.

    The alternate Touring spec size of 195/55R16 has a circumference of 76.8", hence the tire diameter and circumference are in principle identical to 185/65R15.

    Also notice that spare tire size of 125/70R16 has a circumference of 71.9". This is an error of 6%, and combined with the spare tire often being underinflated below the 60 psi spec, can cause the skid control ECU to have a fit as it notices one wheel with the spare tire rotating much faster than the other three.
     
    #6 Patrick Wong, Mar 16, 2019
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  7. dolj

    dolj Senior Member

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    +1 to Patrick’s comments regarding this.
     
    #7 dolj, Mar 16, 2019
  8. moshbit

    moshbit Junior Member

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    so, just to let folks know, i bought a set of four michelin energy saver + tires on ebay for 380 after taxes, seemed like a good deal. got the 195/65/15 size. i'll let you all know how it goes when i get them installed hopefully later next week.
     
    #8 moshbit, Mar 17, 2019
  9. edthefox5

    edthefox5 Senior Member

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    So with the higher sidewall height percentage at 205 what is the offset at 60 mph? 1-2 miles?
     
    #9 edthefox5, Mar 17, 2019
  10. Patrick Wong

    Patrick Wong DIY Enthusiast

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    4% error, so 2.4 mph low.
     
    #10 Patrick Wong, Mar 17, 2019
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