Do KM3s run undersize like KM2s did? - Jeep Wrangler Forum
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Old 01-12-2019, 03:37 PM
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Do KM3s run undersize like KM2s did?

I've been running BFG tires for years now. KM2s (35s & 37s) KO2s (37s)
They all have been undersized - 37s measure more like a true 35 then 37.
Has anyone had experience with the 38in KM3s? If so what do they actually measure in diameter?

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Old 01-12-2019, 04:10 PM   #2
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I have 37x12.5R17D KM3s and they have a rolling diameter of 36”

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Old 01-12-2019, 05:43 PM   #3
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Quote:
Originally Posted by MoabCarl View Post
. . . Has anyone had experience with the 38in KM3s? If so what do they actually measure in diameter?
I don't see a 38" KM3 listed at https://www.bfgoodrichtires.com/tire...errain-t-a-km3.

The following 17" tire sizes and diameters are listed:

315/70R17-E - 34.4" diameter measured on 9.5" rim, rev/mile = 604

35x12.50R17-E - 34.5" diameter measured on 10" rim, rev/mile = 602

37x12.50R17-D - 36.5" diameter measured on 10" rim, rev/mile = 569

39x13.50R17-C - 38.5" diameter measured on 11" rim, rev/mile =540
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Old 01-12-2019, 06:47 PM   #4
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They also have a 37x12.5R17 in Load Range C.
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Old 01-12-2019, 09:47 PM
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I incorrectly listed 38in. I meant to say 39in (x13.5x17).

Thanks for all the replies.

If anybody is running the 39in size can you tell me the actual rolling diameter?
Thanks again.
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Old 01-12-2019, 09:49 PM
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BTW
The actual rolling diameter of my 37x13.50x17 KO2 on a 9in wide rim is 35 inches.
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Old 01-14-2019, 08:39 AM   #7
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The listed tire sizes are correct.

You must remember that the manufacturer measures on a specific width wheel, at a specific PSI, and they include the bulge of the sidewall.

You and I measure only in a straight line, and usually with the weight of the Jeep on the tire also. So naturally we're going to get a different measurement.

It's not that the listed sizing is wrong. It's that there are different ways of measuring tires.
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Old 01-14-2019, 11:37 AM   #8
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Quote:
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. . . You must remember that the manufacturer measures on a specific width wheel, at a specific PSI, and they include the bulge of the sidewall. . . .
Which is why I included the measured rim size with the published diameters in Post #3.

Most, but not all manufacturers inflate to the tire pressure providing the maximum load carrying capability when measuring on the mounted rim, i.e., 35 psi for a P load rated tire, 50 for a C load rated tire, 65 for a D load rated tire and 80 psi for an E load rated tire.

While the tire diameter listed by the manufacturer may be useful for comparing tires and estimating axle clearance, I find the published revolutions per mile to be more useful for comparing tire sizes at the keyboard and the "rolling" or "loaded" radius more useful for measuring tires on the ground. Simply measure from the ground to the hub center.

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