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Need to be schooled on how tire 'size numbers' work.....

Discussion in 'Chevy Trucks' started by ACA L&L, Dec 21, 2011.

  1. ACA L&L

    ACA L&L Senior Member
    Messages: 362

    ok I dont need to know which tire to buy,I need help determining the tallest tire i can buy for my truck, I thought i had the size thing all figured out then i read something that made me question what i thought i knew. I have 2 trucks, 2011 dodge 2500(stock size says 245/75/17...........chevy 3/4 ton says 265/75/17..........I want to buy a taller size tire, not a wider tire, i thought the 285/75/17 would be best choice for all the trucks, but i read that some people were using 235/717.............What number or numbers determine the height of the tire, i want to buy taller/skinnier tires for year round use/ plowing/towing/driving/ etc. Can some one school me on how to order tires online, i refuse to pay Discount tire prices anymore for something you can buy at treadwright for less than half the price........
  2. kimber750

    kimber750 PlowSite Veteran
    Messages: 4,678

    If I remember correct 245 would be the width. Now the 75 is a percentage of the 245 which is what the side wall height is. Of course 17 in the wheel diameter. This is until you get to tires that use the actual measurements for tire size. 33x9.5x15, this would be 33 inches tall, 9.5 inches wide on a 15 inch wheel.

    This was how it was explained to me many many moons ago.
  3. ACA L&L

    ACA L&L Senior Member
    Messages: 362

    Thank you.....so not using the actual tire numbers ....would a 235 85 17be taller than a 285 75 17? Or does the 285 make it wider and taller? if it does then im on the right track, if not, i may have to go to discount and fake buy some tires, then come home and order them.....Thanks for feedback
  4. 87chevy

    87chevy Senior Member
    Messages: 557

    285 is gunna be a 33, almost a 34. where the 235 is a 32.
  5. cubanb343

    cubanb343 Senior Member
    from ERIE
    Messages: 637

    First number is the width. Second is the aspect ratio which i believe is percentage of the first number gives you the sidewall. and obviously third number is rim diameter.

    285 / 75 / 17 would be 285 mm = 11.2 inches width of tire, 75 percent of 285 is 213.75mm which equals 8.42 inches. 8.42 x 2 is 16.84 plus 17 equals 33.84 inches tall, by 11.2 wide i think.

    235 / 85 / 17 would be 9.25 inches wide, 32.7 inches tall. Confusing? You bet
    Last edited: Dec 21, 2011
  6. 87chevy

    87chevy Senior Member
    Messages: 557

    11.6 Thumbs Up get it right. jeez.. haha jk man, close enough. Hopefully he gets the point.

    It's safe to assume a 285 is gunna be right around 33 inches. a 265 is around 31-32
  7. IMAGE

    IMAGE Sponsor
    Messages: 1,747

    A 285/75/17 will have 213.75mm of sidewall (285x.75). that sidewall x 2 = 427.5mm of tire. There are 25.4mm per inch. So 427.5 / 25.4 = 16.83" of tire. Then add in your 17" of rim. and you get a tire 33.8" tall

    A 235/85/17 will have 199.75mm of sidewall (235x.85). that sidewall x 2 = 399.5mm of tire. There are 25.4mm per inch. So 399.5 / 25.4 = 15.73" of tire. Then add in your 17" of rim. and you get a tire 32.7" tall

    The 285 tire will be about 2" wider than the 235 tire. I very much prefer the 235 over a 285 for plowing. The skinny tires bite better and handle better in snow/ice.
  8. IMAGE

    IMAGE Sponsor
    Messages: 1,747

    damit, I got distracted while I was typing and you guys beat me too it!
  9. ACA L&L

    ACA L&L Senior Member
    Messages: 362

    I got it!! At least the part about the 285 being taller and wider than the smaller skinnier tire....I have a new respect for the corner tire shop....