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  1. #1
    JK Newbie
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    Default Tire Size Modification 285/70/17 - 285/75/17 - 305/70/17 - 295/70/17

    Hi all

    Please explain to me the difference between these tires size



    I have a headache already trying to decide on which tires to get for my stuck rubicon.

    I do know I will be buying wheels spacers with my new tires I get, Please helpppp.

    pictures will be awesome
    Last edited by pabl0007; 06-18-2012 at 11:44 AM.
    JK Rubicon Unlimited steal blue

  2. #2
    JK Enthusiast whitejeepjk's Avatar
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    I believe the 75's are taller, considered a 34 inch where 70' are a 33. I run the 285 70 17 with spacers

  3. #3
    JK Super Freak CerOf's Avatar
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    Quote Originally Posted by pabl0007 View Post
    Hi all

    Please explain to me the difference between these tires size



    I have a headache already trying to decide on which tires to get for my stuck rubicon.

    I do know I will be buying wheels spacers with my new tires I get, Please helpppp.

    pictures will be awesome

    the first number, which is the larger, is the width of the tread in mm. the second number is a ratio. The sidewall height is 70% of the width. IF the second number is 65, then it is 65% of the width.

    the final number, is the rim size. The size of the hole in the tire for a simple explanation.


    285/70R17 for the most part, measure about 32.8" tall and about 11" wide. (every manufacturer differs a bit, but this seems to be a good average and is based upon my direct experience with a BFG M/T km2)

    285/75R17 is a 33.?" where the ? is a number I honestly don't know. It is often referred to as a true 34" tire. It is also about 11" wide.

    The 305/70R17 will be about the same size as the 285/75R17.


    A 305/65R17 is about the same size as a 285/70R17. It is about 2/10th" smaller. The wide increases to 12" though with a 305. This makes a HUGE!!! difference in the size of the tread blocks and the size of the voids. The larger tread blocks and larger voids make it MUCH better off-road.

    I've run 235, 245, 255, 265, and now 305 section width tires and by far, the 305 width wins hands down for off-road performance.


    As a general rule, the second number will always be a multiple of "5." For each increment of "5" you go up, you gain almost an inch. For each increment of "5" you go down, you lose almost an inch.


    the same is true for the section width but based upon increments of 10. Assuming the aspect ratio stays the same, for each increase of 10mm in the width, you gain almost an 1" in height.

    285/75R17 is essentially a 34" tire
    285/70R17 is essentially a 33" tire
    285/65R17 is essentially a 32" tire


    305/65R17 is essentially a 33" tire
    305/70R17 is essentially a 34" tire
    305/75R17 is essentially a 35" tire


    285/75R16 is essentially a 32" tire
    295/75R16 is essentially a 33" tire
    305/75R16 is essentially a 34" tire

    so on and so forth. You can see the pattern and apply it accordingly. Real world numbers do vary slightly, so only use this as a general rule.
    '09 Rubicon Unlimited
    305/65R17 BFG M/T KM2 on 17x9 rugged ridge
    AEV 3.5"
    Shrockworks midwidth
    XD9000i



    '02 WJ 3" OME/spacer lift and lots of other stuff.(rip)
    '94 ZJ 4" of lift F=>R and lots of other stuff too. (rip)

  4. #4
    JK Freak Rich6700's Avatar
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    Google tire calculator and you will be able to see the difference between the tire sizes.
    Hope this will help you out.

  5. #5
    JK Super Freak Rule18's Avatar
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    Quote Originally Posted by CerOf View Post


    A 305/65R17 is about the same size as a 285/70R17. It is about 2/10th" smaller. The wide increases to 12" though with a 305. This makes a HUGE!!! difference in the size of the tread blocks and the size of the voids. The larger tread blocks and larger voids make it MUCH better off-road.

    I've run 235, 245, 255, 265, and now 305 section width tires and by far, the 305 width wins hands down for off-road performance.


    As a general rule, the second number will always be a multiple of "5." For each increment of "5" you go up, you gain almost an inch. For each increment of "5" you go down, you lose almost an inch.


    the same is true for the section width but based upon increments of 10. Assuming the aspect ratio stays the same, for each increase of 10mm in the width, you gain almost an 1" in height.

    285/75R17 is essentially a 34" tire
    285/70R17 is essentially a 33" tire
    285/65R17 is essentially a 32" tire


    305/65R17 is essentially a 33" tire
    305/70R17 is essentially a 34" tire
    305/75R17 is essentially a 35" tire


    285/75R16 is essentially a 32" tire
    295/75R16 is essentially a 33" tire
    305/75R16 is essentially a 34" tire

    so on and so forth. You can see the pattern and apply it accordingly. Real world numbers do vary slightly, so only use this as a general rule.
    ^^Great info here. Don't forget that actual mounted measurements are sometimes VERY different than the math. My 285/70/17 measures a little bit over 32". that was a bit of a disappointment, but live and learn.
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  6. #6
    JK Super Freak CerOf's Avatar
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    Quote Originally Posted by Rule18 View Post
    ^^Great info here. Don't forget that actual mounted measurements are sometimes VERY different than the math. My 285/70/17 measures a little bit over 32". that was a bit of a disappointment, but live and learn.
    disappointment is also the fact that the Rubi 255/75R17 is not really a 32" tire but more like a 31.2" tall tire.

    But if you think that most tire manufacturers are most likely men...who believe size matters....they will CERTAINLY be prone to exagerate...right?
    '09 Rubicon Unlimited
    305/65R17 BFG M/T KM2 on 17x9 rugged ridge
    AEV 3.5"
    Shrockworks midwidth
    XD9000i



    '02 WJ 3" OME/spacer lift and lots of other stuff.(rip)
    '94 ZJ 4" of lift F=>R and lots of other stuff too. (rip)

  7. #7
    JK Newbie bulldawg1075's Avatar
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    How much does rim width factor into the overall size? For example, I'm looking at getting new 17x9 rims. Theoretically, my stock 30" SR-As will be less than 30" when I add 1.5" to the width of the rims, right? Is there a calculator for sidewall adjustments based on the rim width?

  8. #8
    JK Freak Wandell's Avatar
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    Quote Originally Posted by pabl0007 View Post
    Hi all

    Please explain to me the difference between these tires size



    I have a headache already trying to decide on which tires to get for my stuck rubicon.

    I do know I will be buying wheels spacers with my new tires I get, Please helpppp.

    pictures will be awesome
    Basically these sizes are essentially:
    285/70-17 = 33x11.50
    285/75-17 = 34x11.50
    295/70-17 = 34x12.00
    305/70-17 = 34x12.50

  9. #9
    JK Super Freak CerOf's Avatar
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    Quote Originally Posted by Wandell

    Basically these sizes are essentially:
    285/70-17 = 33x11.50
    285/75-17 = 34x11.50
    295/70-17 = 34x12.00
    305/70-17 = 34x12.50
    Close. 315 is the 12.5"

    305 is the 12" wide
    295 is 11.5
    285 is about 11"
    265 is 10.5"


    I put the 285/70-17 and 305/65-R17 side by side and the 285 was .3" taller in the BFG MT km2. 32.5" and 32.8" respectively.
    '09 Rubicon Unlimited
    305/65R17 BFG M/T KM2 on 17x9 rugged ridge
    AEV 3.5"
    Shrockworks midwidth
    XD9000i



    '02 WJ 3" OME/spacer lift and lots of other stuff.(rip)
    '94 ZJ 4" of lift F=>R and lots of other stuff too. (rip)

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