Tire and Actual Size - JeepForum.com

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post #1 of 6 Old 07-22-2013, 03:28 PM Thread Starter
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Tire and Actual Size

Good evening all.
I have been in stealth mode on here for quite awhile now and finally bought my first Jeep Wrangler and have to kick myself for not doing it sooner.
OK........Here is my question.
I have scoured the posts till my eyes started bleeding and found many helpful post but not to my specifics.
My Jeep came with a 2" BB with Definity Dakota M/T 31x10.50 r15 tires.
I love the aggressive look of the tires on the Jeep but when I took a tape measure to the rubber the tire is actually only 29 1/4" tall. Yes it may sound anal but I would like a true reading on size because I would like to make my Jeep as tall as possible but still be able to park it in my garage.
I have 6" to spare for my Jeep to fit in my garage and would like to put a radial tire on it since this is my DD. I am looking into a 32x10.50 r15 or even 32x11.50 r15 but would like it to be the actual size it states.
Any help on actual sizes would be greatly appreciated.

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post #2 of 6 Old 07-22-2013, 04:12 PM
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Go to the tire mfg's site and look at the tire specs. That will tell you the actual diameter. Just because it says it's a certain size doesn't mean it actually measures that size.

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post #3 of 6 Old 07-22-2013, 04:13 PM
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most tire company list the true tire size on their websites. so pic the particular tire you want, then go to the respective manufacturers website to look at what the true size is.

however tires like the current Definity Dakota's you have now are an off brand tire made by a third party and do not have a manufacturers site to look up info like this.

I.E. my 38.5x16-15 swampers are listed as actual size of 38.2. not much, but still slightly smaller than listed. this is unloaded weight however. by the time i put the weight of my rig on them at 8PSI, the end up at only just over 36" tall. i'd bet unloaded, your current tires are closer to being 30" or just over, but the weight of your jeep causes them to squat some.

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post #4 of 6 Old 07-23-2013, 06:38 AM
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Yeah here is the deal: Tire makers measure from the ground up INCLUDING the bulge of the sidewalls. They also do this on a specific size wheel. Both of these measurements will be listed in their literature and many times it's also on their websites.

You and I measure from the ground up NOT including the sidewall bulge because what we care about is ground clearance, not the actual rubber surface of the tire.

That is why you will ALWAYS measure your tires shorter than what the listed specs on the tire are. If you want a tire that measures 31" tall then you need to buy a 32x11.50-15.

The only exception to this rule is Treadwright. Treadwright uses the same method as you and I, so their measurements listed on the website are all spot-on. But every other tire maker uses the method I described above. It's the standard. Take whatever you read and subtract 1" from it and you'll have a good idea of what it'll measure out to be on your Jeep.

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post #5 of 6 Old 07-23-2013, 06:53 AM Thread Starter
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Originally Posted by WXman View Post
That is why you will ALWAYS measure your tires shorter than what the listed specs on the tire are. If you want a tire that measures 31" tall then you need to buy a 32x11.50-15.
Thank you all for the great information and input, and Thanks WXman for giving me a very good way to think about it when I do purchase something a little bigger.
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post #6 of 6 Old 07-23-2013, 11:22 PM
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Manufacturer's stated height in their specs is for when the tire is inflated to max inflation (I think without a load on the tire). So once it's on a vehicle, no tire will be as tall as manufacturer's stated height, and their stated height is usually less than the height printed on the sidewall.

The important issues IMO are "will it fit?" and "will it work well with your gearing?"

Warning: I often edit my posts a few times to get them complete, or to correct errors.
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