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metric tire size

Discussion in 'The Garage' started by 86chevybanshee, Mar 1, 2005.

  1. 86chevybanshee

    86chevybanshee 1/2 ton status

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    can someone explain to me how to read metric tire sizes? i need it in dumb form.

    and how i can tell how much taller or wider the tire is

    thanks
     
  2. sled_dog

    sled_dog 1 ton status

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    It has to do with aspect ratios. I've explained it a hundred times, and every time I do it makes less sense to me... in fact I can't explain it anymore. I always just search for "metric tire conversion" on google and find something to plug the numbers into ;).
     
  3. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    235/75r15

    235 mm wide (at sidewall)
    75% of width is the side wall height (x2)
    15" wheel

    i can't think of the formula to convert mm to inches right now.
     
  4. sled_dog

    sled_dog 1 ton status

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    the 75% thing is the aspect ratio I refered to. I really don't get why they don't just go the way we do just in metric numbers
     
  5. AkMudr

    AkMudr 1/2 ton status

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  6. az-k5

    az-k5 1/2 ton status

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    Lets start simple with the mentioned P235-75-15. The last number is rim size (15" wheel). The first number is the width of the tire in millimeters. It is not the distance from sidewall to sidewall, but the actual distance to "walk" from one bead bundle up the sidewall, across the tread, down the other sidewall to the other bead bundle. Then the middle number is a percent of the first number as a reference to the actual combinded side wall height (of wich you need to divide by 2 <number of sidewalls>).
    Just buy flotation sizes it is a lot easier to understand.
     
  7. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    ive always been told it was sidewall to side wall.

    i remember the formula now,
    235 / 25.4=9.25 is the width
    75% of 9.25 =6.9375 is the side wall height (from wheel to tread)
    double the side wall height (for 2 sidewalls)=13.875
    add the 15" rim and you get 28.875" tall

    what did that online calculator say?
    28.9?
     
  8. txfiremank5

    txfiremank5 1/2 ton status

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    4lo has a lot of calculators as well, they can be found in the maroon bar.

    http://www.4lo.com/
     
  9. 86chevybanshee

    86chevybanshee 1/2 ton status

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    thanks for the help

    i think buying tires for my 79 is alot easier.

    im buying new tires for my s10 so most tires sizes are in metric
     
  10. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Uhhh, no. Using that definition would make a 235/75R15 about the size of a wheelbarrow tire.......................

    Here's a quick breakdown:

    235 = section width in millimeters
    75 = aspect ratio in %
    15 = rim diameter

    There is 25.4 millimeters per inch

    To calculate width, simply divide the section width by the conversion factor of 25.4:
    235 / 25.4 = 9.25" in width

    For height, the aspect ratio times the section width will give you the sidewall height:
    235 * 0.75 = 176 millimeters, or 6.9"
    For total height, if you start from the ground and go up = 6.9" (sidewall) + 15" (rim) + 6.9" (sidewall) = 28.8"
     

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