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Old 10-26-2009, 02:10 PM   #1
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Wheel and tire confusion

I'm still trying to fiqure height vs. tire size. I'm getting two different answers. Here's the question: Ford 350 2009: If I want a 33" height. If I use 17" Mojave's. I think the mojave's are 9" (Is that correct?) Are the Nitto terra grapplers then 285/70/17E's or 295/70/17E's ?? Thanks for any help. RD

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Old 10-26-2009, 03:31 PM   #2
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Re: Wheel and tire confusion

Tire outside diameter is calculated as follows:

285 = tire width in millimeters.
70 = tire sidewall percentage of width
17 = wheel diameter in inches

Tire O.D. is then:

285 mm / 25.4 mm/inch = 11.22 inches (the tire width)
11.22 inches x 0.70 = 7.85 inches (the tire sidewall)

Tire O.D. = (7.85 inches x 2) + 17 inches = 32.7 inches

Likewise, 295/70/R17 = 33.25 inches

The 9" wheel width shouldn't affect overall diameter.

If your end goal is 33", it looks like you need to decide whether you want just over 33" or just under 33" with these options. I have 305/70/R16 (~32.8") and I rub a lot at full lock, even without suspension activity. Of course there are many other factors, but this might be a case for going slightly smaller.

Good luck.

(corrected my tire size)
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Old 10-26-2009, 05:57 PM   #3
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Re: Wheel and tire confusion

Here's one of the greatest Internet Gems I've ever found:

http://www.miata.net/garage/tirecalc.html

Since you can put in two tires you can directly compare the 33 vs just under, see the width clearly, etc.

Also most tires come in under the colliqually stated size: for example the 33s SMB uses are actually 32.8 inches. Don't get hung up on being a little under on overall diameter, you'll lose some height when the van weight is on the tire anyway.
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Old 10-26-2009, 06:12 PM   #4
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Re: Wheel and tire confusion

the 285s would work just fine. I don't see an E rated Grappler in that size

http://www.nittotire.com/#index%2Etire% ... er%2Esizes
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Old 10-26-2009, 06:22 PM   #5
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Re: Wheel and tire confusion

Quote:
Originally Posted by jage
That sure was easier than my calculator button-pushing...
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Old 10-27-2009, 10:27 AM   #6
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Re: Wheel and tire confusion

Thank you all. I understand now. To go to a 295 as someone suggested to me I would not have a E rated tire. 285 it is for me. I just hadn't looked at the right web sites.
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